US2098442A - Photographic process with exposure diminution - Google Patents

Description

'@v, 9, 1937. L.. 'I'.TRQLND $998,442,

PHOTOGRAPHIIC PROCESS WITH EXPOSURE DIMINUTION Original Filed Aug. l0, 1953 auf /Pfca Patented Nov. 9, 1937 PHo'roGnAPHro PnooEss WITH Expo- SURE DnvnNU'rroN Leonard T. Troland, deceased, late of Cambridge, Mass., by Cambridge Trust Company, executor, Cambridge, Mass., assignor to Technicolor Motion Picture Corporation, Hollywood, Calif., a corporation of Maine Original application August 10, 1933, Serial No.

684,546. Divided and this application November 16, 1935, Serial No. 50,161

s claims. (ci. :a5-2i This application is a division of prior applil It is well known that latent photographic records produced with light of a certain wave length range, if subsequently exposed to rays of a higher wave length, are photographically diminished or retrogressively destroyed in proportion to the intensity of the second exposure This phenomenon is commonly referred to as Herschel effect and is perhaps related to the well known solarization phenomenon which consists in substance in the fact that a prolonged or otherwise very intensive exposure may, after development, result in a blackening of the photographic emulsion to a lower degree than the blackening effected by weaker light intensities. However, whereas solarization depends upon prolonged exposures, the Herschel effect appears to be substantially independent therefrom and Amerely 'dependent upon the cooperation of consecutive exposures with light of different wavelengths. Although scientists do not quite agree upon the exact nature or theory of the Herschel effect, it is an established fact that the effect of an initial or primary exposure upon a photographic emulsion is reversed upon exposure to light waves of higher wave length, herein referred to as secondary. exposure, and that this result is more rapid, certain and proportional to the intensity of the secondary exposure than any effect that'might be obtained with ordinary solarization.-

It has been found that this so-called Herschel eeot lends itself very well to practical application and permits the carrying out of certain photographic operations which could otherwise not be undertaken at all or only with difficulty. These practical applications make use of the iact that the Herschel effect permits the quantitative subtraction of exposures, which subtraction permits the introduction of a new photographic method of the general nature of an inversion of heretofore known photographic procedures, which method in its various possibilities, is of `considerable practical value.

Although it is herein referred to, the Herschel eiect, it is understood that the prescrit invention is not limited to the utilization of this phenomenon as defined at any given stage of development of the photochemical science, (which denitions might very well vary to a considerable extent), but that it embraces, independently of any vproposed theory or explanation, the herein described practical applications of the possibility of diminishing or reducing the intensity of a photographic record by means of a secondary exposure, as defined in the appended claims.

cation Serial No. 684,546, filed August 10, 1933.

The new method will be explained in its generic v aspect as well as in a specic example, with reference to drawing, in which:

Fig. l. is a set of density-exposure curves indieating the eiect of primary and secondary exposures employed in the present method; and

Fig. 2 is allow diagram illustrating the invention as applied to the separation of color records.

In its generic aspect, the invention proposes the combination of pictorial photographic records by means of primary and secondary exposures, whose effect will rst be generally explained. In Fig. l,

, A is the well-known Hurter and Driilield curve,

commonly referred to as H and D curve, of a given emulsion, which presents densities of a developed record plotted over the logarithms of eiiective exposures, that is, over the log (iXt) where z' is the exposure light intensity and t the exposure time, the product being measured in candle meter seconds. Bis a similar curve, signifying the Herschel eect, obtained by varying secondary exposures of a plate, uniformly pre-y exposed to light of a certain Wave lengtli,'to light of a higher wave length. Point b of curve B corresponds to the density obtained with asecondary exposure Zero, that is, to the density of the developed pre-exposed plate not subjected to any secondary exposure. The other points of the drooping curve correspond to developed densities obtained upon increasing amounts of secondary exposure, and it is evident that the ratio of density decrease is fairly uniform over the density range corresponding tothe substantially straight partA of curve A. Curves C, D similarly signify theeect of secondary exposures subsequent to primary exposures which, without secondary exposures, would result in lower densities, c, d, as indicated.

It is therefore apparent that, if a photographic emulsion is exposed to an object iield, certain portions receiving equalprimary exposures which would result in density b, and if three of these portions arethen subjected to diierent secondary exposures h1, h2, h3, for example, through a photographic record, and developed, the densities of these portions will be reduced to d1, d2, d3, respectively, as indicated in Fig. 1.

On the other hand, if pointscf direrent primary exposures, that is, points which would have densities b, c, d, if developed without previous secondary exposure, are subjected to a certain unithan a superposition of densities.

suitable portions of primary and secondary exposure curves can be selected, and since the shapes of these curves can be controlled with reasonable certainty, it is evident that not only can two exposures be subtracted without disturbing the density gradients of the exposures, especially by using the substantially straight line portions of the exposures, but also that the density gradients vof exposures can be changed at will, as will be explained morein detail hereinafter. l

It should be observed that we are herein dealing not with the subtraction of densities, that is, speaking in terms of the H and D curve, the subtraction takes no place between the ordinates of the curves, but that the Herschel effect involves Y rather an arithmetic subtraction of exposures inside the expression (log E) for the abscissas of the curve, as for example, log (e-h) if e signies a primary and h a secondary exposure. It must thereby be observed, however, that it is not generally possible with elementary means directly to relate e and h, due to the different nature of the two exposures, so that the above way of explaining the operation of the Herschel eiect with sets of curves for the primary and secondary exposures is perhaps the preferable expedient for -it is possible to separate superposed records of diiferent color aspects of an object field, which records are contained in the emulsion of a socalled monopack film. By rst copying the records in superposition, then removing one record, and printing the remaining record and the first copy together, it is possible to obtain a separate duplicate of the removed record. However, such methods can only be employed when the records are substantially independent and involve a superposition of separately produced densities in essentially distinct emulsion layers. 'I'hese methods are not applicable where a composite record involves an addition'of interpenetrative exposures in a single emulsion stratum rather When such conditions prevail, the Herschel effect provides -means for the subtraction of a given color record- 'from a composite record of this interpenetrative exposure type, since it permits to subtract exposures rather than densities. A good example of emulsionsbearing interpenetrative exposures i is the front emulsion of a bipack which records the i red color aspect in front of a mainly blue sensitive emulsion, for the purpose of obtaining a sharp red record and transferring the diffusion blur to the blue record whereit is of minor disadvantage. Bipacks of this kind are well known in the art and for example described in British Patent No. 321,998, for Improvements in or relating to three-colour photography, to Thomas Thorne Baker. Bipacks of this type have the outstanding disadvantage that the red recording, and

V--therefore red sensitive 'front emulsion, is necessarily moreor less blue sensitive, so that the red record is always adulterated with a blue record, this adulteration involving, due to its nature, a

summation of interpenetrating exposures rather than a superposition of densities. 'Ihis blue. adulterating exposure is, for obvious reasons, very undesirable, but can be eliminated from the red sensitive front nlm by utilizing the Herschel effect according to the present invention, for example in the following manner:

, The bipack front illm containing the composite red and blue exposure is developed, and a latent composite positive printed therefrom, this printing step constituting a primary exposure in the sense of this term as herein used. This latent record is then exposed, through the conventionally tially pure and unadulterated red record posi-A tive, from which a pure red record duplicate negative can be made, which, with the black illm record, constitutes a. complementary pair of unadulterated color aspect records. It is of course understood that instead of secondarily exposing a latent positive to a. substantially permanent negative, a' latent composite negative, for example, the original negative, can be exposed to a positive, for example, the original back film record.

The emulsions used for practically utilizing the Herschel eifect must be selected with a view to suitability for that purpose. Good results were obtained with customary emulsions, preferably treated prior to use by bathing in a 1 to 2% solution of potassium bromide for about ve minutes, with Subsequent drying. It was also found that dyed emulsions suitable for making gelatine matrices, of the type as described in the same invention eopending application Serial No. 454,973, led May 23, 1930, matured into Patent No. 2,044,- 864 of June 23, 1936, are especially suitable for purposes of the prent invention. The primary exposure may be made with daylight, or with the customary artificial light sources used for photographic negative and positive processes, whereas secondary exposure with light of a wave length of approximately 700 to 780;'. was found to be satisfactory, although experiments with primary X-ray exposures and secondary exposures with white light also gives acceptable results. 'The primary exposures do not substantially differ from ordinary exposures, whereas, concerning duration, it is dlilicult to give exact data for the secondary exposures, since they depend a good deal upon the conditions in each particular case. It was found that an emulsion having received a primary exposure corresponding to a customary printing exposure of about one-half second, gave, in the abovedescribed monopack process, satisfactory results witha secondary exposure through the blue record with light concentrated from a high-power tungsten illament lamp filtered through a illter passing substantially the above vgiven spectral range, for

about five totwenty seconds, depending on the strength of the light source, and the record density. A suitable filter is any of the commercial infra red filters., or a combination of a so-called Dark Theatre Blue" filter and a Selenium Red (Nos. 503 and 242, listed in; the publication entitled Glass Color Filters ofthe Corning Glass Works) glass filter, which transmits practically only infrared light, with a very small percentage of visible deep red.

'I'hls improved bipack (or tripack) method is schematically illustrated in Fig. 2, where W is a bipack with a front lm comprising support S' with red-blue sensitive emulsion E' and a back iilm comprising support S" withblue sensitive emulsion E. Emulsion E contains a red record R' adulterated with a record substantially corresponding to the blue-record B of emulsion E". The two bipack component iilms are nished as usual and a master positive fihn G with emulsion H and support T is then exposed to record R' with light L so that emulsion H receives a latent record K which is a positive of record R and comprises the adulteration of the latter. Subsequently, Without intermediate treatment, emulsion H is subjected to a secondary exposure with high wave length light L' through negative record B. This secondary exposure reduces the latent record K according to a pattern which corresponds to the blue record B', so that the new latent record K does not contain the adulterating blue component which was present in latent record K. Care must of coursebe taken that the secondary exposure of G is so adjusted that not more exposure is subtracted from record H than corresponds to the blue adulteration' of record R'. After development, lm G represents a correct positive K of the red color aspect, which, together with the initially correct blue negative record B' can be further utilized according to conventional methods.

Concerning the illustration of the` invention in Fig. 2, it should be remarked that the record patterns are indicated by varying thickness only (as it would be present, at least substantially, in emulsions having incorporated highly light absorbing substances) whereas these patterns might as Well be represented by varying overall particle distribution.

It has been found that primary exposures with X-rays as mentioned before, and secondary exposures with radiations of higher wave length, which in' this case may be ordinary white light, can be employed advantageously, especially in instances where 'a uniform primary exposure is applied. It has also been found that treatment in certain substances of the class known in the art as desensitizers (as for example phenosafranine) intermediate primary and secondary exposure, inlluences the latent record of the emulsion so as to permit the use of light of substantially the same wave lengths for both primary and secondary exposure. It will be apparent that these phenomena,

as far as their practical application to pictorialy photography is concerned, are in their action quite similar to that of the Herschel eiect which is herein morev particularly described, and that one or the other will be preferably used according to convenience and expediency.

It should be understood that the present disclosure is for the purpose of illustration only, and that this invention includes all modications and equivalents which fall within the scope of the appended claims.

. What yis claimed is:

l. The method of combining photographic records, which comprises making in an emulsion layer of the silver halide type a latent record of an object eld and in register therewith in a second emulsion layer a substantially permanent record of another aspect of the same leld, said rst layer receiving a record component substantially in conformity with said second record,

and exposing said latent record in register through said permanent record with light photographically diminishing said latent record in amounts controlled by the permanent record, thereby diminishing said component in said rst layer.

2. The method of producing photographic records of different color aspects of an object field,

which comprises making in an emulsion layer of the silver halide type a latent positive record of a certain color range and in 'a second emulsion layer a negative record of the same object iield, but of a smaller color range substantially included in the range of said latent record, said rst layer receiving a record component substantially in conformity with said second record and exposing said latent record through said negative record with light adapted photographically to diminish said latent record, whereby said negative'record is substantially subtracted from said latent record, thereby diminishing the color range recorded in said first layer.

3. The method of producing photographic records of different color aspects of an object eld, which comprises making in'an emulsion layer of the silver halide type a latent negative record of a certain color range and in a second emulsion layer a positive record of the same object eld, but of a smaller color range substantially included in the range of said latent record, said first layer receiving a recordcomponent substantially in conformity with said second record and exposing said latent record through said positive record with light adapted photographically to diminish said late nt record, whereby said positive record is substantially subtracted from said latent record, thereby diminishing the color range recorded in said rst layer.

4. The method of producing photographic records of different color aspects of an object eld,

which comprises making in an emulsion layer a record of a certain color range of said object field, making in a second emulsion layer a second record of the same object iield with a second color range that is included in said rst color range, said first layer receiving a record component substantially in conformity with said second record, copying said rst recordon a photographic silver halide emulsion, and exposing said emulsion to said second record in register with thelatentrecord contained therein, with light of a lower wave length than that of the copying exposure thereby .diminishing the color range in said rst record.

5. The. methodI of combining vphotographic records, which comprises superposing two emulsion layers one of which is sensitive to a greater spectral range than the second layer, exposing said layers whereby said rst layer receives an exposure component substantially coniorming to the exposure of said second layer, making a developed record corresponding to the exposure in said second layer, providing a latent silver halide gelatine record of the exposure in said lirst layer, said developed record and said exposure component in said latent record being approximate photographic complementals, and exposing said latent record through said developed record with light photographically diminishing said latent record, thereby diminishing said exposure component in said iirst layer.

6. In the art of color photography the method which comprises superposing an emulsion layer Ainsensitive to red light and an emulsion layer tsensitive to red and to the sensitivity range ofl second layer receives an exposure component substantially conforming to the exposure in said rst layer, making a developed record corresponding to the exposure in said rst layer, providing a latent silver halide gelatine record of the exposure in said second layer, said developed record and said exposure component in said latent record being approximate photographic complementals, and exposing said latent record through saiddeveloped record with light photographically diminishing said latent record, thereby diminishing said component in said second layer.

^ CAMBRIDGE TRUST COMPANY, Executor of the Last Will and Testament of Leonard T. Troland, Deceased.

By A. MEAD WHEELER, Assistant Secretary.

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