US2676101A - Method of reversal processing sound tracks - Google Patents

Description

April 2o, 1954 A. R. ULMER 2,676,101

METHOD OF REVERSAL PROCESSING SOUND TRACKS Filed Dec. 21, 1950 IN V EN TOR.

mired Emmer ,WW/fl/ 'Patented Apr. 1954 TENT OFFICE METHOD OF REVERSAL PROCESSING SOUND TRACKS Alfred R. Ulmer, Dumont, N. J., assigner to Radio Corporation of America, a corporation of Dela- Waffe Application December 21, 1950, Serial No. 202,097

1 Claim.

This invention relates to the production of photographic sound tracks, and particularly to a method of exposing and developing photographic sound tracks subjected to a reversal process of development. it can be used for both original recording and in printing.

In the production of normal black and white sound records, the negative may be properly exposed to provide a density, which, when printed to another predetermined density, will eliminate image spreads which produces distortion and a low signal-tonoise ratio. This may be accomplished by exposing the emulsion so that the light does not penetrate very deeply into the emulsion. Any unexposed silver bromide beneath the exposure and in the areas which are to be cleared are removed by the hypo solution and do not interfere with the light passing through the track when it is printed, if a negative, or when it is reproduced, if a direct positive. It is only necessary that the exposing light should penetrate sufficiently to give the desired track density. Exposure of sound tracks by ultra-violet light has been made to reduce distortion caused by image spread.

necessary that all the silver bromide in the track area be exposed throughout the emulsion layer. This causes excessive image spread and the sound track becomes distorted. Distortion shows up by the elimination or reduction in the high frequency components of the signal recorded and the signal-to-noise ratio suiiers. This is caused by the fact that the first development of the exposed track turns the silver bromide to metallic silver, which is then removed by a bleaching solution. If any of the silver bromide is not eX- posed, it will not be developed to metallic silver, and it will not, therefore, be removed by the bleaching operation. if not removed, it will appear as silver grains in the track areas where `crains are not wanted. To penetrate the emulsion sufficiently for the reversal process, the intensity of the light must be much greater than for normal black and White processing causing excessive image spread and improper denition of the boundary between the opaque and transparent sections of a variable area photographic sound record.

The present invention is directed to a method of exposing and developing emulsions by a reversal process to produce photographic sound records of the same quality as the present standard form of black and white records produced by first obtaining a negative and then printing However, when using a reversal process, it is` to a positive. It involves making a clearing exposure of the emulsion, but not in accordance with the pre-exposure shown in U. S. Patent No. 1,840,351 of January 12, 1932. This patented method of pre-exposure provides linearity between the exposure and density of the nal record. rhe present invention is directed to variable area or variable density recordings, but particularly applicable to variable areas, wherein not only is a sharper line of separation produced between the opaque and transparent areas or a variable area track, but the line of separation is in the proper place. The clearing exposure may be made before or after the signal exposure.

The principal object of the invention, therefore, is to provide an improved method of producing sound records by the reversal development process.

Another object of the invention is to provide an improved method of exposing and developing nlm emulsions by a reversal process to produce photographic sound tracks.

Although the novel features which are believed to be characteristic of this invention will be pointed out with particularity in the appended claim, the manner of its organization and the mode of its operation will be better understood by referring to the following description, read in conjunction With the accompanying drawings, forming a part hereof, in which:

Fig. 1 is a diagram showing the amount oi image spread in a photographic emulsion inr ace cordance with the intensity ofthe exposing light.

Fig. 2 is a series of diagrams disclosing the old form of producing sound records by a reversal process.

Fig. 3 is a series of diagrams showing a method oi exposing and developing emulsions by a reversal process in accordance with the invention, and

Fig. 4 is a diagram illustrating a modiiication of the invention shown in Fig. 3.

Referring to Fig. 1, the depth of an emulsion d is shown as being between its outer surface 6 and its inner surface i', which is in contact with a base B. This diagram of Fig. 1 is being shown for purposes of explanation, and has been taken from page 871i of the bool; entitled The Theory of the Photographic Process, by Dr. C. E. Kenneth Mess, published in August, 1942. The exposing light rays d are impressed on the emulsion perpendicularly to the surface 6, one boundary being at the point Iii. The lines between and parallel with surfaces 6 and '1 up to a line perpendicular to surface S at point I0, and which then curve toward surface represent different amounts of exposure of the emulsion 5. rlhus, if the exposure is represented by line l I, there will be an image spread between the point i2 where the line touches the surface and the point 1?. That is, the exposure will be the same between points i@ and I2 as it is from surface t to line H.

II" the amount or" exposure corresponds to line lil, the image spread then will be between the point I 5 and the point is, the depth of the exposure following the straight and curved portions of the line. if the exposure is such that the entire emulsion is exposed to the base E, it will cause image spread. as indicated by the lines terminating at points il, and IS. When sound tracks are made by the negative-positive process, the negative exposure is just sufficient to provide the proper den ty with the minimum of image spread. When the negative printed, the diagram of Fig. l is reversed, so that the points l2, i5, il, i8, and is lie on the left side or line iii and neutralization is obtained lt is to be understood that each silver bromide particle must receive a certain amount of light to cause it to be developed to metallic silver. If it receives less than this amount of light, it will not be affected by the developing solution. However, due to internal reflection, certain particles receive sufficient light and others do not, so partial clearing is produced. Furthermore, since exposures are additive, two successive exposures, each insuiicient of itself, may expose the particle sumciently to make development effective. This is the principle or" the present invention.

Referring now to Fig. 2, each of the various diagrams from a to e, inclusive, show a photographic sound recording emulsion .9.5 between the surfaces 2i and 22 on a base 23. A beam of light 25 oi a certain width is shown striking the surface 2i of the emulsion perpendicularly, and the passage thereof through the emulsion is represented by the lines 21: and 23, it being noted that the effect of the exposure diverges due to internal reflections of the light within the emulsion so that at the base the width of the emulsion surface effected is greater than the width of the light beam. By lines 29 and fili, the extent of the image spread as described with respect to Fig. l is indicated, so that the areas between lines 2?-29 and between lines ZS--l have also been exposed, although this exposure may be tapered so that actually no deiinite line as shown exists. The cross-hatching of the emulsion indicates silver bromide.

Referring now to Fig. 2b, the effect of the irst developing step is shown, the developer being of the elon-hydroquinone type which turns the silver bromide to metallic silver, as indicated by the stippling Si, while the remaining silver bromide stays unchanged. It will be noted that the areas Ell-2e and of 2q. have been developed to metallic silver, which be slightly tapered, while there may be some silver bromide in these areas. The actual width of the exposing beam 25 has been indicated by the short boundary lines extending from the surface El.

The next step in the process is shown in Fig. 2c, wherein the nlm is subjected to a bleaching solution of the potassium ferricyanide-potassium bromide type, wherein the metallic silver is dissolved, as shown by the clear area 32, but the silver bromide is unchanged. However, because of the variable exposure in the 2?--29 and {i3-3i) areas of Fig. 2a, some silver bromide may exist therein.

The next reversal step is to expose Ythe entire sound track area to uniform light, as shown in Fig. 2d. The lm is then developed again, as shown in Fig. 2b, which changes the silver bromide to metallic silver, as shown at 3l in Fig. 2e. As seen in Fig. 2e, the clear area is much wider than the original exposing beam, which means that high frequency peaks of sound modulations will be reduced if not entirely eliminated. Also, there is actually no sharp line of separation between the clear area 32 and the silver areas 37. This method also produces a fog on the base which necessitates increasing the gain during reproduction, and thus, introduces background noise.

The present invention permits a sound track to be made by a reversal process without the deleterious effects just described in connection with Fig. 2. The new step is shown in Fig. 3a, whereby an emulsion 3'3 has an outer surface te and an inner surface 35 in contact with a base 36. Y In these series of diagrams, the silver bromide is again shown by the cross-hatching and the metallic silver isV shown by stippling. in Fig. 3c, a clearing exposure of the entire sound track area is shown, which, for purposes of illustration, is shown by the line 38, and which penetrates approximately one-half the distance through the emulsion. The line t8 is shown wavy to indicate that the eiect of the exposure will not be a sharply defined line, but through internal reflections will be graduated. This clearing exposure is insufficient of itself to permit the silver bromide particles to be turned to silver if developed, although it could be of suiiicient value. The illustrations, however, are with a, clearing exposure light below the developing value.

The second step is to expose the emulsion to light modulated by sound signals, as shown by the beam of light 40 in Fig. 3b. However, since the area within the line 38 has already been exposed and exposures are additive, the intensity of the sound track modulations may be much less than in Fig. 2a to properly expose the emulsion above the horizontal portion of the line 3d and also the remaining portion of the silver bromide below. the horizontal portion of the line 38. Since the light intensity is low, image spread is small, and, instead of being of the amount shown at 27--29 and 23--30 in Fig. 2a, is now reduced to very narrow regions between the lines 39. Since these regions are narrow, they cause very little deterioration of the final sound track..

After the exposures shown in Figs. 3a 3b, the emulsion is subjected to therst developing step shown in Fig. 3c, corresponding to the step shown in Fig. 2b, whereby the exposed silver bromide is turned to metallic silver 13, as shown by thestippling. The bleaching step, as shown in Fig. 3d, removes the metallic silver, leaving a clear area di and the silver bromide. The second exposure, shown in'Fig. 3e, exposes the remaining silver bromide, which will be turned to metallic silver 42 when again developed, as shown in Fig. 3f. It will be noticed in Fig. 3f that the width of the clear area 4l is substantially the same as the width of the light beam di?. and the lines of separation between the area il and areas 42 are sharp compared with the lines between similar areas in Fig. 2e.

The preliminary exposure, as shown in Fig. 3a, may -be made with either white or ultra-violet light, which is also true of the modulating exposure shown in Fig. 3b and the benets of the use of ultra-violet light Vmay thus be obtained. This is not true of the process shown in Fig. 2,

because of the high intensity required to fully expose all the silver bromide. Furthermore, the second exposing light, such as shown in Fig. 3e, may be controlled, and for certain lm emulsions, this light could also be ultra-violet, The process thereby permits high quality sound records to be obtained by the reversal process.

A modiiicaticn of the invention is Shown in Fig. 4, wherein a signal light beam @5 is impressed on an emulsion 46, while a clearing exposure has been impressed on the emulsion through the base 41, as shown by line f. In this instance, the clearing exposure light may have sufcient intensity so that no further exposure is necessary by the signal light. Thus, the intensity of the signal beam 45 may be very low, just suicient to get through the remainder of the emulsion, which will reduce the image spread along lines 50, while none will exist below these lines. That is, the narrow areas between the pairs of line 39 in Fig. 3b would be reduced to a minimum. Thus, if a lm base is such as to permit a clearing exposure to be made through it, this is the preferred method.

Although the invention has been described using one form of reversal process, it is also applicable to other reversal processes where the final opaque regions are silver sulphide. The invention has been illustrated with a light beam of a certain Width corresponding to a certain signal amplitude, but the signal beam may be any width up to that of the sound track area. Furthermore, either the clearing exposure or thel signal exposure may be made first.

I claim:

The method of producing a photographic sound track by the reversal process comprising exposing a photographic emulsion through the base supporting said emulsion to a degree wherein approximately one-half the depth of said emulsion next to said base becomes developable, then directly exposing said emulsion to light modulated by sound, said light being of an intensity such as to just render developable the remaining half depth of said emulsion, then developing said emulsion to change the exposed emulsion to metallic silver, then removing said silver, then uniformly again exposing said emulsion to render the remainder of the emulsion developable and again developing said emulsion to change said last exposed emulsion to metallic silver.

References Cited in the file of this patent UNITED STATES PATENTS Great Britain July 29, 1935

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