US2660528A - Hypersensitizing photographic film developer - Google Patents

Description

Patented Nov. 24, 1953 HYPERSENSITIZING PHOTOGRAE'HIC FILM DEVELOPER Bobbie J. Schultz, Hollywood, Calif.

No Drawing. Application March 25, 1952, Serial No. 278,493

3 Claims.

This invention relates to the art of developing, in photographic negatives (black and White), the latent image produced therein by exposure to actinic light.

Virtually all photographic negative film used today in the production of black and white photographs utilizes, as a light sensitive coating, an emulsion of a silver halide in a gelatin film. The most commonly used halides are the silver bromides and the silver chlorides, and the present invention deals particularly with the development of latent images in coatings containing crystals or grains of halides as the light sensitive ingredient thereof. With conventional developing practices, good negatives can be obtained only from film that has been sufficiently exposed Within the range of exposures specified for the film. Underexposed film results in a negative having either no image or only a faint image, from which it is impossible to obtain a satisfactory print.

The present invention deals with the problem of recovering a satisfactory negative from an underexposed film, and its general object is to provide a hypersensitizing developer for intensive developing of an underexposed film so as to obtain an adequately developed final image from the underexposed latent image on the film.

The fact that latent images in underexposed film can be developed into satisfactory negatives by a two-stage process starting with a normal developing operation (resulting in a final image that is wholly unsatisfactory, i. e. entirely too undeveloped) followed by a secondary developing operation known as intensification, is generally known. Intensification involves depositing additional silver on a previously developed weak negative image resulting from an ordinary developing process using a standard developer. Intensification processes have not proven to be fully satisfactory. All of them are objectionable because they involve two stages of development instead of only one, and are therefore more time consuming and expensive. One such process, which utilizes a second exposure of the latent image to a light of low intensity, has the further objectionable result of grading down or fogging the entire image. Another such process, in which the latent image is exposed to ammonia fumes, also causes some fogging. Still a third, utilizin exposure to mercury vapor, is impractical due to the length of exposure time required.

The present invention is directed toward a hypersensitizing process (a single operation development rather than to a multiple stage intensification process). Many attempts have been made, of course, throughout the history of photography, to increase the sensitivity of developing processes so as to extend the range of utilization of underexposed latent images in the production of satisfactory final images in a single development operation. One of the problems that has been faced in all such endeavors, is that of obtaining simultaneously, in a single development operation, satisfactory final images from both underexposed and adequately exposed latent images.

A convenient measure of amplification of image development obtained from intensification and hypersensitizing processes, over the results obtained from conventional development practices, is in terms of increase in the speed" of the film as indicated by the results of such extraordinary processes, over the normal specified speed of the film as determined by the results of standard development practice. Based on this measure of improvement the greatest increase in film speed previously obtainable through hypersensitizing has been in the neighborhood of five times normal film speed. That is to say, hypersensitizing has, up to the present time, been capable of utilizing a latent image produced at approximately one fifth the exposure period required for a good final image under standard development practices. The best results obtained in the use of intensification processes have been an increase to ten times normal film speed.

It is widely understood that the commonly available emulsions of today must have a certain minimum exposure in order to obtain any picture at all. According to all photographic development exposure theories, the standard ratings of film speed or emulsion sensitivity are based on the proposition that the exposure cannot fall below the minimum determined by the Weston rating of the film, if satisfactory pictures are to be produced. Any substantial deviations in exposure, outside the range indicated by the Weston rating, is commonly understood to result in no image at all; or, if presently known hypersensitizing or intensifying or overdeveloping methods are practiced, only the high lights (areas of maximum exposure) will build up to a printable density. To my knowledge there has never been previously made available any developer or method whereby more than ten times the normal exposure rating the normal exposure time) can be utilized in exposing film, and even with the use of the known hypersensitizing or intensifying methods, the high lights usually build up so 3 much faster than the shadow areas that the results are entirely unsatisfactory Or unusable in the minimum exposure portion of such range of reduced exposures.

The common understanding that it is impossible to drop much below the commonly understood minimum exposure for any given film, is so widespread as to be known generally as the threshold of exposure below which there is insufficient light striking the negative to produce any image. The threshold is commonly plotted on a graph as a toe of a curved line indicatin film speeds, processing time, etc. It is my belief that this toe may be simply the top one in a series of such toes rising steplike from a point far below anything that has previously been considered at all within the range of possibility. If this belief is correct, current film speed ratings may represent, not the minimum, but rather, the maximum of exposure that can be given to a negative.

The invention involves the discovery of a hypersensitizer which gives excellent results far beyond the range previously attained as indicated above. To illustrate the results, I have, using my developer, obtained negatives of good quality from exposures up to one hundred times the specified Weston ratings for such film (i. e., down to one percent of the degree of exposure specified for such film). These results have been obtained in research utilizing principally the Eastman Kodak Companys Plus -X roll film (which has a Weston rating of 50 for standard exposure and development practices), in unbelievably short exposure periods of between 4000 and 6000 Weston. In this connection it will be understood that an exposure taken at the Weston rating of, e. g., 5000 Weston, will admit only one percent of the light which is admitted in an exposure of 50 Weston rating. Accordingly, it is apparent that the present invention produces an increase in ratio from the :1 ratio, the highest ratio previously attained, to a 100:1 ratio, ten times as great.

Furthermore, I have succeeded in obtaining these results without sacrificing resolution of the image, i. e., without substantial distortion of the relation between highlights and shadows.

With the foregoing in mind, the general object of my invention is to provide a hypersensitizing developer and a hypersensitizing concentrate for producing such developer, which produces a much higher degree of hypersensitizing than has hitherto been possible, such as to obtain good negative images from slight exposures produced as low as one hundred times below standard specified exposure levels.

The problem of the photographer has long been that of sacrificing one thing for another (e. g., shutter speed for depth of field, etc.). The present invention opens up an entirely new field of possibilities for the photographer, in making it possible to utilize as low as one percent of the light formerly considered necessary for a proper exposure. By thus making it possible to reduce exposure time to undreamed of shortness, the invention provides a wide latitude of selection of small camera apertures for sharpness of detail, depth of field, etc. In fact, it makes it possible to approach the ideal aperture, i. e. the pin-point type of camera aperture which is in focus for practically every depth from the most distant up to within but a few inches of the camera objective.

With the great increase in film speed which my developer makes possible, a photographer can now take pictures under lighting conditions which at 4 present virtually make it impossible to obtain any picture at all. For example, good pictures may be obtained on heavily clouded days, under twilight conditions, and even by moonlight, using conventional film now useable only for daylight pictures or pictures taken with the aid of strong fioodlights, or flashlights.

It is of course necessary to properly relate the development of the negative to the exposure conditions. This can be done either by shortening the development time, for exposures of greater intensity than the minimum which is made possible by the invention; or by adjusting the exposure for adopting a substantially standard development practice such as to utilize maximum film speed without departing from optimum results in the resolution of the image, and adjusting to fit such optimum development practice. Thus the taking of pictures on a heavily clouded day, with apertures inside the range ordinarily used for full sunlight exposures, would be common practice, and for full sun exposures, the aperture would be stopped down far below the common range of apertures, or the shutter speed would be increased to a point far above the normal range of shutter speeds, or some combination of aperture reduction and increased shutter speed would be utilized. The taking of action pictures necessitating extremely fast shutter speeds would likewise become possible with the standard snapshot film now provided, and it would not be necessary to utilize the high speed films commonly used for such action pictures.

All of the foregoing improved results are included among the objects of my invention.

My improved hypersensitizer concentrate is characterized generally by the use of formic acid as an active ingredient thereof. More particularly, the invention is characterized by the combination of formic acid with ammonia, glycerine, and 6-nitrobenzirnidizole (a substance commonly used as an anti-fog agent) to produce the concentrate.

The following examples illustrates typical hypersensitizer concentrates embodying the invention:

Example I Spirits of ammonia-10% NHiOH64 drams Formic acid-HC0.0H32 drams fi-nitrobenzimidizole (dry)-12 grains Glycerine-4 drams The functions of the several ingredients are as follows:

Ammoniaactive hypersensitizing agent Formic acidactive hypersensitizing agent 6 Nitrobenzimidizole-fog inhibitor Glycerinebinder for ammonia The G-nitrobenzimidizole which I have employed, is, specifically, Eastman Kodak Company Anti-Fog #2, in powdered form, sometimes referred to as A. F. #2.

Preparation.The hypersensitizer concentrate is prepared as follows: first, the prescribed amount of 6-nitrobenzimidizole powder is dissolved in four ounces of formic acid. This is S It is to be understood that the proportions of the ingredients may be varied to some extent within the scope of the invention. The range of possible variation i indicated by the following additional examples of the concentrate.

Example I] solution NH4OI-I64 drams BOOGIE-32 drams G-nitrobenzimidizole (dry)--12 grains Glycerine-4 drams Formaldehyde (HC'OH)-1 to 8 drams This formula will provide for additional hardening and help to prevent swelling of the emulsion, for use in extremely high temperature processing. The degree of hardening may be controlled by the amount of HCOH added to the standard formula.

The addition of the HCOH to the formula necessitates an increase in the amount of hypersensitizer solution added to the standard developer. Such increase in the amount of concentrate to be added to the standard developer may ordinarily be determined as roughly twice the amount of HCOH that is added to the concentrate, i. e., for each 2 drams of HCOH that is added to the concentrate, 4 additional drams of the concentrate will be added to the developer.

Example III 10% solution NH4OH21 drams HC0.0 I-I32 drams 6 nitrobenzimidizole (dry)--l2 grains Glycerine4 drams This formula does not produce quite as intense an action as the formulas of Examples I and II.

Example IV NH4OH'128 drams HC0.0H32 drams fi-nitrobenzimidizole (dry)-12 grains Glycerine-4-8 drams DEVELOPER The concentrate is utilized by adding a small quantity thereof to a standard developer. For example, in the use of the concentrate disclosed in Example I above, from 27 to 60 drops of the concentrate are added to 16 oz. of standard developer.

In developing negatives in the developer thus produced standard developing practice is followed except that the developing time is from one and a half to two times the normal developing time. An 80 F. temperature is observed in the developer solution.

The following examples illustrate the developer of my invention:

Example I WaterI-I2Oat 125 F.l quarts Elon (methylaminophenol sulfate)- HO'CGH (NI-ICHs) /,;H2S04360 grains Sodium sulfite-NazSQsJ7H2O4 ounces HYdI'OQHIDODMGH (OI-I) 2-400 grains Sodium oarbonateNa2OOs2 ounces Potassium bromideKBr-200 grains Ammonia solution10% NH4OH2 drams .5 %6-nitrobenzimidizole2 drams Formic acidHC0.0H--2 drams Hypersensitizer concentrate (Example I above)- 6 drams Water up to 2 quarts Preparation-In the preparation of the developer, the chemicals named above are dis solved in the order named, starting with the 1 quarts of hot water, then adding the elon, sodium sulfite, hydroquinone eto., successively. As the final step, the indicated quantity of cold water is added to the solution to dilute it to the proper strength. A precipitate of calcium, elon and sulfite may be formed during the mixing process. If this occurs, the precipitate should be carefully filtered out of the solution. After the solution has cooled to room temperature, the developer is ready for use.

Where an emphasized tanning efiect is desired, the sodium carbonate may be replaced by sodium sulfate, without sacrificing the function of the carbonate. Thus the developer may comprise:

Epulmple II It is to be understood that the quantities of chemicals in the hyper-developer may be varied and the results remain fairly constant over some range of deviation; provided a near proportion is maintained.

The following example will illustrate:

Example III Elon (methylaminophenol sulfate)- HOCsH4 I-I2SO4-180 grains Sodium Su1fiteNa2SO3.7I-I2O2 ounces Hydroquinone-CsH4(OH)2-400 grains Sodium carbonate-NazCOs1 ounce Potassium bromide-KBr-l00 grains Ammonia solution-l0% NHlOH-2 drams .5 %-6-nitrobenzimidizole2 drams Formic acid-HCO.OI-I1 drams Water to make2 quarts Aerosolounce H2O'1 quarts Example IV Elon (methylaminophenol sulfate)- HOCsHe 1/2H2S04-29O grains Sodium sulfite--Na2SO3.7HzO8 ounces Hydroquinone-C6II4(OH) 2--1 /2 ounces Sodium carbonateNa2COel ounces Potassium bromide-KBr--400 grains Ammonia solution-40% NH4OH1O drams .5%-6-nitrobenzimidizole-1O drams Formic aoid-HC0.0H9 drams Water to make2 quarts Aerosol--2 ounces I-IzO-N/ quarts Example V Water-I-hO-at F.1 quarts Elon (methylaminophenol su1fate) HOCsI-Ie (NI-ICI-Ia) /2H2SO'4-360 grains Hydroquinone-CsH4(OI-I) 2400 grains Sodium carbonate-Na2CO32 ounces Potassium bromide-KBr200 grains (Example I Ammonia solution-10% NH4OH-6 drains Formic acidHC0.0I-I4 drams .5%-6-nitrobenzimidizole3 drams Water to make-2 quarts Aerosol-1 ounce The addition of Aerosol merely increases the life of the developer and allows it to go into action on the negative faster and more evenly. Aerosol is a trade-name for one of many wetting agents which break the surface tension and allow the liquid to saturate more evenly, quickly and completely.

USE OF DEVELOPER For best results, the user will indulge in some experimentation with the solution. However, as .a starting point, good results may be obtained by developing for approximately twenty minutes, at 80 F. negatives which have been exposed at 4000 Weston ratings. A correspondingly longer developing period will be utilized for lower film speeds.

It may be noted from the foregoing Example I of the developer, that several of the ingredients of the concentrate (for example the ammonia and nitrobenzimidizole ingredients) are repeated in the concentrate and in the developer to which the concentrate is added. Formic acid is added to the developer separately and also as an ingredient of the concentrate. One of the functions of the concentrate is to increase the proportions of the common elements.

In the foregoing developer the hydroquinene functions in its normal capacity as a reducing or developing agent, reducing the silver halide In any developing process, it is probably true that, when the developing process is arrested, the various grains of the emulsion will be arrested in various stages of conversion from silver halide to metallic silver, depending upon the amount of light which has been received by the respective grains. That is to say, the more highly exposed grains will undoubtedly be converted into silver more rapidly, during the development process, than the less highly exposed grains. In the hypersensitizing and hyper-developing process which results from the use of my improved hyper-developer, it is believed that the same general relationship between the progres sive stages of development of the more highly exposed grains and the less highly exposed grains, is maintained, but that the developing process for all of the grains is speeded up so that the same or equivalent results are secured from greatly underexposed emulsion as is secured by ordinary developing methods from emulsions with standard exposures. Stated somewhat differently, it now appears that even very, very slight exposures of the emulsion grains with the various graduations of exposures resulting from the differences in light coming from the dark and light parts of the subject, can be utilized to start' the process of developing the various grains, and that, through the use of the hyperdeveloper these very slightly exposed grains may be brought up through a relatively long stage of development from the very slightly exposed condition thereof, to the final stage of development in which a satisfactory negative is produced, the same as, in standard developing procedures, the much more heavily exposed grains, but with the same relative differences of exposures in the light and dark areas of the picture, will be brought, to substantially the same final stage of development, through a range of development which may be considered as only a small fractional, terminal portion of the entire range of development utilizing my improved developer.

This theory appears to be consistent with the fairly widely accepted theory concerning the nature of the conventional film developing process. According to that theory, the silver halide grain is a crystal consisting of a regular assemblage of positively charged silver ions and negatively charged halide ions. It is assumed that each crystal of silver halide contains interstitial silver ions, that is, ions displaced from their normal position in the crystal. Light rays impinging upon the crystal liberate electrons from the bromide ions. These electrons attach themselves to the sensitivity centers, which are believed to be nuclei of silver sulphide scattered throughout each silver halide crystal. As the electrons attach themselves to the sulphide sensitivity centers, they acquire a negative charge. Consequently they attract the positively charged interstitial silver ions, which move up to the centers, where they combine with the electrons to form neutral atoms of silver. These atoms, in conjunction with the sensitivity centers, constitute the latent image.

If this theory is correct, it will be apparent that the action of the developer is to carry forward the incipient conversion of silver halide to neutral metallic silver atoms, which has been initiated by the exposure of the silver halide crystals to light. It will also be apparent, if we assume that the degree to which the conversion has been advanced by the light exposure is proportional to the amount of light falling on respective grains, that the various sensitivity centers Will, in the latent image, be in various degrees of advancement of the conversion process. It also seems logical to assume that, as the conversion is carried forward in the developing process and enters the visual image stage wherein the density of the collodial metallic silver which has been collected around the sensitivity centers, becomes suii'icient to bring out the characteristic black color of the collodial silver, that each sensitivity center will maintain a relative position of advancement of the process, corresponding to its relative position of advancement in the latent image.

Based upon the foregoing assumptions, it may be considered that, in the development of a visible negative from a latent image on a very slightly exposed film, using my improved developer, that the developing rocess simply commences at a much earlier stage in the evolution of metallic silver from silver halide at the sensitivity centers, and that, at the very terminal stage of such development, the process parallels the conventional development process beginning with a latent image resulting from a heavy exposure.

I claim: 7

1. A photographic negative developer containing methylaminophenol sulfate, sodium sulfite, hydroquinone, sodium carbonate, potassium bromide, ammonia, 6-nitrobenzimidizole, and water and, in addition, formic acid functioning as an hypersensitizing agent for developing full images irom latent images which, according to exposure rating of the film, are highly underexposed.

2. A photographic negative developer containing methylaminophenol sulfate, sodium sulfite, hydroquinone, sodium carbonate, potassium bromide, and water and containing in addition, as an hypersensitizing agent for developing full images from latent images which, according to exposure rating of the film, are highly underexposed, a combination of formic acid, ammonia, 6-nitrobenzimidizole and glycerin in the following proportions:

Spirits of ammonia-40% NH4OH-64 drams; Formic acid-I-IC0.0H--32 drains; B-nitrobenzimidizole (dry)12 grains; Glycerine--4 grams.

3. A developer for intensified development of photographic negatives, comprising a combination of a standard developer having the following ingredients in the proportions stated:

and, as an hypersensitizing agent for developing full images from latent images which, according to exposure rating of the film, are highly underexposed, a small portion of a hypersensitizer concentrate additive consisting of the following ingredients in the following proportion:

Spirits of ammonia-10% NH4OH-6 l drams; Formic acid--HC0.0H32 drams; 6-nitrobenzimidizole (dry)-12 grains; G1ycerine 4 grams.

BOBBIE J. SCHULTZ.

No references cited.

Claims (1)

1. A PHOTOGRAPHIC NEGATIVE DEVELOPER CONTAINING METHYLAMINOPHENOL SULFATE, SODIUM SULFITE, HYDROQUINONE, SODIUM CARBONATE, POTASSIUM BROMIDE, AMMONIA, 6-NITROBENZIMIDIZOLE, AND WATER AND, IN ADDITION, FORMIC ACID FUNCTIONING AS AN HYPERSENSITIZING AGENT FOR DEVELOPING FULL IMAGES FROM LATENT IMAGES WHICH, ACCORDING TO EXPOSURE RATING OF THE FILM, ARE HIGHLY UNDEREXPOSED.