Ansco Colorpak / Ansco Color, type 735
1946 – 1950
Subtractive 3 color: Chromogenic monopack, reversal 35 mm, 12 ASA
(Ansco Division of General Aniline and Film Corporation)
Original Technical Papers and Primary Sources
Ball, J. Arthur (1946): Quality in Color Reproduction. In: Hollywood Quarterly, 2,1, pp. 45–49, on pp. 47–48.
Bates, J. E.; Runyan, I. V. (1949): Processing Control Procedures for Ansco Color Film. In: Journal of the Society of Motion Picture and Television Engineers, 53,7, pp. 3–24.
Duerr, H. H.; Harsh, H. C. (1946): Ansco Color for Professional Motion Pictures. In: Journal of the Society of Motion Picture Engineers, 46,5, pp. 357-367.
Forrest, J. L. (1945): Machine Processing of 16-mm Ansco Color Film. In: Journal of the Society of Motion Picture Engineers, 45, Nov. 1945, pp. 313-326.
Harsh, H. C.; Schadlich, Karl (1949): Laboratory for Development Work on Color Motion Pictures. In: Journal of the Society of Motion Picture and Television Engineers, 53,7, pp. 50–57.
Sweet, Monroe H. (1945): The Densitometry of Modern Reversible Color Film. In: Journal of the Society of Motion Picture Engineers, 44,6, pp. 419–435.
Beyer, Friedemann; Koshofer, Gert; Krüger, Michael (2010): UFA in Farbe. Technik, Politik und Starkult zwischen 1936 und 1945. München: Collection Rolf Heyne, on p. 54. (in German)
Cornwell-Clyne, Adrian (1951): Colour Cinematography. London: Chapman & Hall, 3rd. ed., on pp. 390–392.
Ray, Reid H. (1949): Use of 35mm Ansco Color Film for 16mm Color Release Prints. In: Journal of the Society of Motion Picture Engineers, 53,8, 1949, pp. 143–148, on pp. 144–148.
“Dank als Kriegsbeute beschlagnahmter Patente und mitgenommener Rezepturen sowie der Mitwirkung von Agfa-Fachleuten bei Konkurrenzunternehmen eroberte das in Deutschland ausgearbeitete Farb-Negativ/Positiv-Verfahren auch andere Länder: Aus Belgien kamen die sehr ähnlichen Gevacolor-Filme, aus Italien Ferraniacolor, aus der Schweiz Telcolor, in den USA folgten Ansco-Color und Kodak Eastman Color, in Japan Fujicolor.31
LITERATUR- UND QUELLENANGABEN
31 Gert Koshofer: Die Agfacolor Story, in: Weltwunder der Kinematographie, 5. Ausgabe, Potsdam 1999, S. 69ff.; Gert Koshofer: COLOR Die Farben des Films (1988), S. 109ff., 119ff.”
(Beyer, Friedemann; Koshofer, Gert; Krüger, Michael (2010): UFA in Farbe. Technik, Politik und Starkult zwischen 1936 und 1945. München: Collection Rolf Heyne, on p. 54.) (in German)
“The distinctive feature of any additive method is that all three elements at all times retain their independence. Unfortunately, additive methods of reproduction are very inefficient in their use of available light. As a result, “subtractive” methods are used exclusively for prints on paper and for motion picture theater projection.
Subtractive methods employ images in dyes or transparent pigments in a manner very similar to that of an artist who paints a picture in transparent water colors on paper. In photographic methods of reproduction the three subtractive elements may either be stacked up in successive layers or intermingled in one and the same layer. But in whatever manner the subtractive images are made, we encounter the unfortunate fact that all available dyes and pigments, even though they are selected to absorb light principally in one of the primary bands, also absorb considerably in the other primary bands. Therefore, the three dye or pigment images are no longer mutually independent. Furthermore, prints on paper must be viewed in daylight or incandescent lamplight, and motion picture prints must be viewed by carbon arc light. All these various light sources emit energy at all visible wave lengths so that the components of a subtractive print must collectively control the entire spectral range. Both of these circumstances require a whole series of compromises which extend back to the original camera analysis filters, and the practical camera filters for subtractive methods are quite different from the theoretical camera filters which are correct for additive methods.
These compromises destroy the delicate distinctions between colors reproduced by the subtractive method. Oranges and reds tend to appear as tones of the same intermediate orange-red. Yellow-greens and blue-greens tend to appear as tones of the same average green, and green-blues and blue-violets tend to appear as tones of the same average blue. These compromises and the resultant loss of distinction are not necessary in additive reproduction, and thus the results obtainable thereby, so far as delicacy, accuracy, and ranges are concerned, are superior to those of the subtractive methods.
Even the best of present-day subtractive processes, such as Technicolor prints and Kodachrome and Anscocolor originals, all suffer from these compromises. By appropriate compensations these processes are quite acceptable to the eye if there is no direct comparison with the original subject.
To add to the difficulties of reproducing color, when any subtractive method is used twice in succession – first for the original and again for the print – there is a compounding of the troubles, and still further compromises and compensations are entailed. As a result somewhat inferior reproduction is obtained. During the war we have seen many pictures in which subtractive prints have been made as blow-ups from a subtractive original, the latter frequently being on 16 mm. film. In such cases there is a compounding of the subtractive confusions mentioned above, and, of course, also a relaying to the final print of any quality defects which may be in the original 16 mm. film.
If now a “duping” step is attempted in the same manner (i.e., original, dupe, and final print all subtractive), the final result shows the effect of three distortions and three attempted compensations. The result is frequently horrible. Many of these defects, it should be understood, are fundamental and not to be eliminated by mere refinement of technique.
Since even a first-generation subtractive print is full of defects and compromises, real progress in color quality can scarcely be expected to come from a struggle with the second and third generations of the same defective family. Rather is it necessary to avoid, if possible, the compromises required by even the first-generation subtractive image. Experimental work is in progress in many quarters to eliminate, or at least to mitigate, the usual subtractive defects, to improve the methods of application of such compensations as are necessary, and also to make additive methods, or their equivalent, applicable in some of the necessary stages of a complete process. The ideal is a final print which will combine the light efficiency of the subtractive print with the quality of an additive reproduction.”
(Ball, J. Arthur (1946): Quality in Color Reproduction. In: Hollywood Quarterly, 2,1, pp. 45–49, on pp. 47–48.)
“However, when the client asks for 35-mm and 16-mm prints in three-color, there has been actually only one process the industrial producer had to turn to, Technicolor. Technicolor production, as everyone knows, is not geared especially to industrial production budgets; besides, very often, industrial location work is complex and camera equipment must be as mobile as possible with minimum crews for extensive traveling. This paper does not purport that Technicolor does not meet the requirements, but that Technicolor is not an economical color process for certain types of industrial color production which this paper presents.
Of course, two cameras, one 16- and one 35-mm, might be used simultaneously on all shots, but this calls for an extra crew, extra equipment, extra film cost, lighting problems, and double editing, conforming, and handling all through the production. The purpose of this paper is to present a method one production company used to solve the request for 35- and 16-mm color release prints and to do it in an economical manner.
The basic 35-mm color film used was Ansco color camera film, Type 735, which is an integral subtractive color film of the reversible type. Introduced in 1946, this camera film is balanced for exposure by daylight and the best color rendition on exteriors is obtained in bright sunlight.1 For interior work, high-intensity arc lamps with Y-l filters are recommended for key-lighting with the fill light supplied by white-flame arc broads, such as Duarcs, or “CP” lamps filtered with MacBeth Whiterlite filters.
In our studio we have obtained good results with incandescent lighting equipment, using CP lamps with MacBeth Whiterlite filters, although extremely high total wattage must be used as an exposure level of 1000 foot-candles at f/2 with color temperature of 5400 degrees Kelvin is required. That is better understood when one knows that the film speed is rated thus: ASA Exposure Index 6; Weston, 5; and General Electric, 8. Ansco UV-15 or UV-16 filter or the Wratten 114A filter is recommended for all exteriors and interiors.1
Ansco color camera film, Type 735, may be used in regular 35-mm professional cameras without any conversion and, therefore, Bell and Howells, Mitchells, or even Eyemos are satisfactory for production work. That fact was very important in the requirement of the industrial production job to be described. There were assignments to be met within three months’ time, scattered from California through Colorado, Texas, Kentucky, Mississippi, Illinois, Iowa, Minnesota, North Dakota, and Oregon; and half a dozen cameramen, with a wide variety of equipment, had to be assigned to shoot the color footage under a great variety of field conditions. These varied from flying over the great wheat fields of the Pacific Northwest with an Eyemo in order to climb the steep hillsides to film the harvest; to standing in almost knee-deep water in the rice fields of Mississippi, no place for heavy cumbersome color cameras, and the Eyemos and lighter Bell and Howells came in handy and turned in creditable color photography. In some locations cameras had to be secured on top of moving machines, and one Mitchell was even tied down inside the grain tank atop a huge combine moving over rough ground.
No photography was planned before 10:00 o’clock in the morning, and seldom after 4:30 in the afternoon, and bright sunlight was a prerequisite. As a result, a fairly evenly exposed original camera film was obtained. Approximately 15,000 feet were shot during those three months. It is recommended that one single-emulsion number be used on each production as there is, as in all color processes, some color-balance change in succeeding emulsion runs. It was also found that pleasing effects and good definition in dark areas were obtained with cross, and even partial, backlighting. Naturally extra caution was taken in exposure reading and our camera crews carefully considered the subject before deciding on a lens stop.
After the original camera film was exposed, it was shipped to the Houston Color Laboratories in West Los Angeles for developing and printing “daily.” During the past 10 months this laboratory has been processing approximately a half-million feet per month of Ansco color film, and is equipped to turn out a daily print within 48 hours. The processing of Type 735 camera film is almost identical to a description by Forrest,2 except for a somewhat shorter developing time in both the first developer and the color developer.
In making a daily print from the original camera film, each scene is not timed for density and color balance, but an over-all average printer exposure and an average filter balance are determined and the daily is printed. The printing stock is Ansco color release film, Type 732, also a reversible-type film of relatively low speed, very fine grain, and special sensitization for printing.3
When the daily print is received, it is edited as in black-and-white production, and the track is recorded. This step is followed by re-recording sound effects and musical background. At this point a word should be given about the type of track best suited for Ansco release printing. Excellent results with no loss in reproduction volume have been obtained using the direct-positive method of final recording. A studio recorder, Radio Corporation of America PR 23, was converted to handle either negative or direct-positive recording. Otherwise in negative sound recording, with a positive track furnished for printing, some method has to be devised to realign the track placement because the track must be on the opposite side of the film for printing a reversible type of color system.
Conformation of the original camera film with the edited daily work print follows and lap dissolves or other effects may be inserted as there is Ansco color Type 132 duplicating film and Ansco color Type 154 masking film available for making effects on optical printers. When conformation is complete and the re-recorded direct-positive film is synchronized, this material is delivered to the laboratory to prepare a composite print. In timing the original, the laboratory now times each scene for printing, as in black-and-white procedure, except that each frame of the timing strip has a different filter balance and there are several density balances made on each scene.4 From these strips, a timing number and a filter combination are selected to print each scene. The first print from the assembled negative, known as the answer print, has scene-for-scene density and color correction. The Bell and Howell printers used have been remodeled to provide a light source of 3200 degrees Kelvin for printing the Ansco color release positive, Type 732, and for inserting filters into the light source quickly and for the rapid changing of these filters during printing. This answer print is shipped to the producer for approval and if color balance on certain scenes needs changing, a second answer print is processed. After an approval has been obtained, release prints are ordered and the 35-mm print requirements are supplied.
MAKING THE 16-MM COLOR PRINT
Each 35-mm release print is carefully inspected, and one is selected to be used as the master for the production of the 16-mm release prints by optical reduction to Kodachrome. The original camera film, Type 735, which is being used for 35-mm printing cannot be used inasmuch as available reduction printing equipment is not equipped to make filter changes scene by scene. However, the 35-mm release print is color-balanced scene for scene and, therefore, it can be used as the master for the 16-mm reduction printing. The 35-mm print is first carefully timed, although very few light changes are needed, and with the proper filter pack, customarily used in printing Kodachrome duplicates, a 16-mm reduction print is made. A Depue reduction printer, using a 250-watt lamp, with a blower added to dissipate the heat for filter protection, is used for this work. Although the print being used for the picture reduction work is a composite print with track, this track is not used for sound printing. A 35-mm direct-positive variable-area track with additional compression for 16-mm reproduction was recorded for this assembly immediately after the re-recorded track was made for the 35-mm prints. An RCA 35- to 16-mm optical reduction sound printer, running 180 feet per minute, prints the sound on the 16-mm Kodachrome print stock.
Although the resulting 16-mm Kodachrome release print is a second-generation print, it is quite acceptable, and compares favorably with 16-mm Kodachrome contact duplicates from 16-mm Kodachrome originals. This is, no doubt, due to the fact that the original was shot on 35-mm film and that a reduction print results in better quality than a 16-mm contact print.
Approximately fifty 16-mm reduction prints each of two 2-reel pictures were made by this method, and the 35-mm Ansco release print used did not show any noticeable scratches, shrinkage, or warpage from its runs through the Depue printer. Both 35- and 16-mm prints were released within three weeks after the day the last scene was photographed – an excellent record for fast service, and credit is due the two laboratory crews who helped make such a record possible.
In the production of commercial motion pictures, problems of location work, economy of operation, making the best of conditions as they are found in the field, and transportation of photographic equipment have a direct bearing on the increased use of business films. Therefore, a practical solution in producing commercial films in 35- and 16-mm color has been desired for a number of years. Although the method just described of how 35-mm Ansco professional color film Type 735 was used to produce 35- and 16-mm release prints may be improved in the future, the method still did make possible an acceptable color process, with distinct production advantages, to a large user of commercial films. It is the belief of the author that the “difficult can be done immediately; the impossible takes a little longer.” An answer to the difficult was found; perhaps the “impossible” will be solved in the years ahead of us.
(1) H. H. Duerr and H. C. Harsh, “Ansco color for professional motion pictures,” J. Soc. Mot. Pict. Eng., vol. 46, pp. 357–368; May, 1946.
(2) J. L. Forrest, “Machine processing of 16-mm Ansco color film,” J. Soc. Mot. Pict. Eng., vol. 45, pp. 313–327; November, 1945.
(3) Garland C. Misener, “Notes on the use of Ansco color camera film Type 735,” Motion Picture Division, Ansco Company, Binghamton, N. Y., 1949.
(4) Data furnished by Robt. F. Burns, Laboratory Manager, The Houston Color Laboratories, West Los Angeles, Calif., 1949.”
(Ray, Reid H. (1949): Use of 35mm Ansco Color Film for 16mm Color Release Prints. In: Journal of the Society of Motion Picture Engineers, 53,8, 1949, pp. 143–148, on pp. 144–148.)
“Ansco Color for Professional Motion Pictures*
H. H. Duerr and H. C. Harsh**
Summary – The 3 new Ansco Color Films which are designed for producing full color million picture release prints are described. These films are (1) Ansco Color Type 735 (Camera Film), (2) Ansco Color Type 132 (Duplicating Film), and (3) Ansco Color Type 732 (Release Film). Methods for making second generation dupes, special effects, lap dissolves, etc., are discussed, and the procedure for printing sound tracks is outlined.
The basic principles of the Ansco Color process have been described previously. We will, therefore, limit the discussion of these principles to a brief review of the fundamentals of the process so far as they are necessary for the proper understanding of the application of Ansco Color to motion picture production.
The Ansco Color process is an integral subtractive color process using the method of dye coupling for the production of dye images in a multilayer material. Colorless color-forming components are incorporated in the emulsion layers. It is the unique and very important property of the color-formers in the Ansco Color process that they are of a molecular structure which renders them nondiffusing. The color-formers are immobilized in their respective emulsion layers and do not bleed into adjoining layers.
The layer arrangement of Ansco Color Reversible Film is shown in Fig. 1a and 1b. The film base, which can be either cellulose nitrate or acetate, carries an antihalation layer, followed by the red-sensitive emulsion layer. This emulsion layer also contains a colorless dye-forming component which, upon development in a suitable color developer, develops an image in color, complementary to the color sensitivity of the layer. In the case of the red-sensitive emulsion layer, the color is blue-green or cyan. For reasons of simplicity, this layer is usually referred to as the “cyan” layer.
The green-sensitive middle layer contains a color-former which, upon development, produces a magenta image, therefore called “magenta” layer. A yellow filter layer, coated on top of the magenta layer, absorbs all blue light, which would normally affect also the cyan and magenta layer, and therefore has to be filtered out in order to obtain the desired separation of color in these layers. The top emulsion layer is blue-sensitive only and the nondiffusing color-former in this layer develops to a yellow image. This layer will be referred to as the “yellow” layer.
The dye formers or color-formers in all 3 layers have been carefully selected so that they develop to a cyan, magenta, and yellow color, respectively, in one color developing step. This greatly simplifies the processing of Ansco Color Film and makes it possible to have the complete processing done by the consumer with developing equipment which is very similar to that regularly used for black-and-white reversible development.
The fundamental principles of the Ansco Color process are applicable to a great variety of color products. Ansco Color Reversible Film for daylight and tungsten light has been in use for some time in the form of 16-mm and sheet film. These materials are being manufactured for use primarily for direct projection and, therefore, have gradation characteristics which make them particularly well suited for this purpose. These film types, however, are not very satisfactory for the motion picture industry, where the requirements are essentially different. The most important requirement for a color transparency suitable for 35-mm motion pictures is that it lends itself to the printing of first and second generation duplicates with a minimum loss in color brilliance and fidelity.
These considerations call for a camera film which is quite different in gradation, color balance and other characteristics from the regular Ansco Color Film. Ansco Color Type 735 is the new film material designed and developed to meet these specific requirements of the motion picture industry.
Fundamentally, Ansco Color Type 735 is quite similar to the regular Ansco Color Film and the layer arrangement is the same as shown in Fig. 1a. It differs from this film primarily in that the gradation is considerably softer, the grain is finer, and the color balance is purposely slightly off-neutral. Fig. 2 shows a comparison of the H and D curves of Ansco Color Type 735 and the regular Ansco Color Daylight Film Type 235. This new material is designed to provide a film for exposure in the camera which is ideally suited for making release prints on Ansco Color Release Film Type 732. Ansco Color Type 735 is not intended for projection and its use in motion picture practice should parallel the use of the original negative in black-and-white motion pictures. Because it is a positive color transparency, it is, however, possible to judge immediately after development the color rendition and other pictorial effects of the scene.
Ansco Color Camera Film is available on both nitrate and acetate base, and designated 735 and 835, respectively.
Ansco Color Camera Film is balanced for exposure by daylight and the best color rendition on exterior exposures will be obtained in bright sunlight. For studio exposures, excellent results are obtained with key-light provided by high-intensity carbon arcs which are modified by Y-1 gelatin filters and fill-light by tungsten lamps for color photography filtered with Macbeth Whiterlite filters. The spectrogram shown in Fig. 3 gives the relative response of the film to the visible region of a daylight spectrum.
Suggested meter settings for the exposure of Ansco Color Type 735 are Weston 8, or G. E. 12.
For optimum print results, it is desirable that the Ansco Color original be slightly underexposed or somewhat heavier in density than is the usual practice when exposing a transparency for screen projection. The reason for preferring a heavy original is to maintain as much of the exposure as possible on the straight-line portion of the H and D curve and avoid inaccurate color reproduction which can result from exposures which fall predominantly in the toe region.
The processing of Ansco Color Type 735 is almost identical to that which has previously been described by Forrest.1 The only variation is a somewhat shorter developing time in both the first and the color developer. In this connection we believe it is indicative of the simplicity of the Ansco Color process that several laboratories have converted existing black-and-white machines for the processing of Ansco Color Film and in all instances very little difficulty has been encountered. At least in one case, the very first roll of Ansco Color Film which was developed on a converted black-and-white machine was of excellent quality.
(1) Direct Prints from Original Color Transparency. – As previously mentioned, the release printing stock for an Ansco Color Type 735 original is Ansco Color Release Film Type 732. This film is also of the reversible type and while fundamentally similar to the other Ansco Color reversible films, it is characterized by a relatively low speed, very fine grain and special sensitization for printing. This printing stock can be developed to a high maximum density to obtain optimum color brilliance. Fig. 4 shows a typical H and D curve for this film. Fig. 5 shows a wedge spectrogram of the Ansco Color Release Film. There are relatively sharp sensitivity peaks in the green and red regions and a partial gap between these peaks. Good separation of the peaks of sensitivity is very essential in a printing film in order to obtain faithful color reproduction.
Ansco Color Release Film will be available on both nitrate and acetate base and designated 732 and 832, respectively.
Most motion picture printers which are suitable for printing present-day black-and-white positive stocks can be readily adapted to print Ansco Color Release stock. If not already available, the following features should be provided on a printer to make it suitable:
(1) A light source which operates at a color temperature of approximately 3000 K.
(2) A means for inserting printing filters into the light path quickly and conveniently.
(3) A condenser lens system for the light source in order to concentrate the light at the aperture. Ansco Color Release Film, with the printing filters in place, will require 2 to 4 times the light needed for printing black-and-white positive fine-grain stock.
(4) It is good practice to provide an air blast or fan as a means of dissipating the heat from the lamp house in order to avoid damage to the filters and film.
Using a regular black-and-white printer with the modifications just described, the printing of the Ansco Color original onto Ansco Color Release Film requires the insertion of filters to balance the color quality of the light source. A standard series of Ansco color compensating filters, in varying densities of yellow, magenta, and cyan, are available for this purpose. Considerable control of the color balance of the release print is possible by the selection of these printing filters.
The processing of Ansco Color Release Film is carried out on the same developing machine and in the same solutions as used for the Ansco Color original. Adjustments of the developing times to suit the particular machine conditions are necessary.
So far we have discussed the camera film and the release printing film for the Ansco Color process without referring to methods for including optical lap dissolves, wipes, and special effects where second generation duplicates of the original Ansco Color will be involved.
(2) Prints from Duplicates. – It is generally recognized that in color reproduction each printing step results in a noticeable degradation in color. For this reason it is desirable to reduce the number of printing operations in color photography to a minimum. However, in motion picture practice it is not feasible in many instances to print from the original color transparency. This is particularly true in those cases where special effects, such as lap dissolves and wipes, have to be incorporated in the sequence of the picture, also for foreign releases where it is essential that a master dupe is available for release printing. Two methods for making master dupes have been worked out for this purpose.
The first method consists of straightforward optical printing of the Ansco Color original onto Ansco Color Type 132 Duplicating Film.
The duplicating stock Type 132 requires about the same exposures as the release stock 732, that is, approximately 2 to 4 times the light needed for regular positive fine-grain stock. The film is processed in the same solutions as the Type 735 original. The developing time in the first and second developer is shorter. A duplicate is obtained which is substantially equal in contrast to the camera original. This first generation duplicate can then be interspliced with the original and used for release printing on Ansco Color Type 732 Release Film. The H and D curve of the Type 132 Duplicating Film is shown in Fig. 6.
The fact that the original as well as the dupe and the release print stock can all be developed in the same machine and in the same solutions represents a very essential simplification of the Ansco Color process. As pointed out before, there are differences in the developing times for these 3 color films, and in order to allow a more exact comparison, the approximate developing times are listed:
The developing times shown are only approximate, since the exact time depends very largely upon the machine speed and the solution agitation in the machine.
There will be an inevitable loss in color brilliance in the second generation duplicate prepared by this method. However, the loss is probably not serious enough to preclude its use for certain lap dissolves, wipes, and other special effects, especially if the subject of these special effects is of such a nature that a very critical judgment of color rendition is not possible. Because of the loss of color brilliance by this method, it is not recommended for making full-length master dupes. For this purpose and where good color reproduction is desired on special effects, the following second method is preferred.
(3) Prints from Masked Duplicates. – In order to counteract the color degradation, the second method of making a master dupe employs a black-and-white silver mask. It is not the purpose of this paper to go into the details of the theoretical requirements of masking, but rather restrict this discussion to the recommendation of a simple procedure for masking Ansco Color Type 735.
A special low-shrink, panchromatic, black-and-white film has been developed for masking in connection with the Ansco Color process. The characteristics of this material are such that the required masking densities are obtained with the least amount of critical control. For this reason, the gamma infinity of the material is adjusted to the masking requirements. In Fig. 7, the characteristic H and D curve of this special masking film is shown. In order to insure good registration, the same printing equipment should be used for the printing of this color correction mask which later on is used for the printing of the masked master dupe. In Fig. 8, a schematic outline of the type of optical printing equipment which can be used for this purpose is shown. The essential features of a suitable printer are 2 synchronized intermittent movements with register pins which are combined with the necessary optical equipment.
In making the black-and-white mask, the original and the mask are run in contact in the camera head while using the projection head empty as a light source only. A yellow filter is placed into the light path while printing the masking film. After the mask has been developed in a regular negative developer, the master dupe is printed. In this operation, the original is run in the projection head and optically registered with the black-and-white silver mask which is now run in the camera head in contact with the Ansco Color Type 132 Duplicating Film.
The printer must be equipped with a viewer or other suitable means so that the registration of the original and the mask can be checked before printing the master dupe. The conformed master dupe can be made in one printing operation, even though special effects may be necessary. In the case where special effects that require mattes are to be inserted, these should be run in the projection head with the original. This method will yield a conformed master dupe that will show little or no loss in color brilliance.
This masked master dupe is then used for printing of the release prints, using Ansco Color Type 732 Release Film in a regular continuous printer with provisions for the insertion of filters and a stronger light source, as described earlier.
So far, only the pictorial part of the process has been discussed, but it is realized that methods of obtaining good sound are of equal importance. Since the release printing stock is a reversible film, a positive black-and-white track is required for printing. The ideal way to obtain the black-and-white positive would be a direct-positive recording. However, equipment to record to a direct positive is not generally available, and the following method has been found almost equally satisfactory and is the one recommended. The recording head of the sound equipment is moved so that the negative recording is obtained on the opposite side of the film. This negative is then printed onto black-and-white positive stock, which will then have the sound track in the proper position for printing directly onto the Ansco Color Type 732 Release Film in the conventional manner.
Dye tracks, especially those obtained by the dye coupling method, have a relatively low absorption in the infrared region. Therefore, the conventional infrared-sensitive photocell, for example type 868, is not too well suited for these dye tracks and a loss in volume amounting to approximately 6 db is encountered. This loss in volume, while serious, still comes within the range where adjustment can be made by fader setting on most 35-mm projection equipment. Fortunately, within the last few years the development of blue-sensitive photocells has progressed and cells are available today which are ideally suited for dye tracks and will play normal silver tracks with approximately the same volume so that interchange of tubes is not required. This photocell, which is at present available from the Radio Corporation of America, is designated as the 1P-37.
Summarizing, the Ansco Color process is capable of producing full color motion picture release prints, including commonly used effects, with only minor changes in equipment which is now used extensively for black-and-white motion pictures. We believe that the Ansco Color process offers a relatively simple method for making motion pictures in color which can be readily mastered by those skilled in black-and-white motion picture techniques.
1 Forrest, J. L.: “The Machine Processing of 16-Mm Ansco Color Film,” J.
Soc. Mot. Pict. Eng., 45, 5 (Nov., 1945), p. 313.
*Presented Oct. 17, 1945, at the Technical Conference in New York.
**Ansco, Binghamton, N. Y.”
(Duerr, H.H.; Harsh, H. C. (1946): Ansco Color for Professional Motion Pictures. In: Journal of the Society of Motion Picture and Television Engineers, 46,5, pp. 357–367.)
“Processing Control Procedures for Ansco Color Film*
By J. E. Bates and I. V. Runyan
Ansco, Binghamton, New York
Summary – Reproducible processing of Ansco color film requires continuous control of the solution compositions. Early experience showed that frequent change of processing solutions was necessary to maintain consistency. New replenisher formulas are described which together with sensitometric controls and occasional chemical analysis have proved successful for maintaining the processing solutions in a satisfactory condition indefinitely. Color-balance differences resulting from varied types of agitation, depending on the processing equipment, may be adjusted by changing the chemical constitution of the first developer.
The continuous processing of Ansco color film requires control of speed, gradation, fog, D-max., and other variables common to the processing of black-and-white films, but with the complicating factor that these variables must be kept constant in each of three superimposed emulsion layers.
When this color film was first introduced, frequent changes of processing solutions were advised to prevent the deteriorating effects of aging and exhaustion. With experience, methods of processing control gradually have evolved using continuous replenishing procedures controlled by sensitometric and analytical tests. This paper presents an outline of the essential control steps necessary at each operating stage of a processing laboratory. Through the use of these practices an experienced control man can maintain a set of processing solutions indefinitely. Tests are outlined not only for actual machine operations but also to check raw chemicals and individual mixes of solutions. Although essentially designed for motion picture laboratories, the basic methods are also applicable to roll- and sheet-film processing units, and with different developer replenishers, to the processing of Printon.
I. Basic Control Methods
Three general control methods, photographic, analytical and pH, are recommended for the various testing operations. The necessary tests are outlined briefly in Fig. 1. For simple solutions such as short stop and hardener, simple pH tests suffice. For developer solutions and actual machine controls, both photographic and analytical tests are necessary. A chemical standard is used as the basis for all tests. A supply of high-purity chemicals should be maintained as the processing standards and type solutions should be prepared from these chemicals with accurate mixing.
A. pH Tests
pH is controlled with Coleman or Beckman Laboratory Model pH instruments using glass-calomel electrode systems. Other instruments of equal sensitivity would suffice. All pH readings including those of developers given in the paper are based on the use of a normal glass electrode. It is recognized that the use of an electrode introduces sodium ion errors due to the high salt concentration of the solution, but in practice, since the salt concentration remains constant, consistent and useful readings are obtained and no attempt is made to correct the data. If a special electrode designed for high salt concentrations at a high pH (10 to 11) is used, the developer pH readings will range about 0.10 higher than indicated in this paper. It is to be emphasized that except for short stop and hardener solutions which are fully controlled by pH, the pH values are used merely as a guide. Solutions can be rejected and trouble located if pH measurements fall outside normal limits, but proper pH does not insure satisfactory performance.
B. Photographic Tests.
These can be divided into two parts: (1) photographic solution control tests, and (2) photographic tests made on the machine during operation.
1. Photographic Solution Control Tests
Tests so termed are used for testing raw materials, solution mixes, and in locating possible sources of trouble with machine solutions. The photographic test consists simply in processing duplicate sensitometric strips of color film through the standard cycle of color-film processing except that the strips are separated at the solution to be tested and one strip run through the sample solution and one through the type solution. These sensitometric strips should be exposed on the same type of color emulsion the machine will process. A supply of film of a single emulsion number sufficient for several months’ control operation should be set aside to avoid too frequent typing in of emulsions. Either time or intensity-scale sensitometry may be used, although intensity-scale instruments are recommended because they give a more accurate indication of a film’s practical performance. The instrument, however, must be capable of highly reproducible results and should be adjusted to produce a color balance close to neutral. Both visual and densitometer measurements are more accurate when made with neutrally exposed film. Latent-image changes in exposed strips are normally of small magnitude. However, it is recommended for optimum consistency that no exposures more than two months old be used for control work.
It is essential that solution testing be done under carefully controlled conditions of agitation, time, and temperature so that the system itself has reproducibility greater than the solution tolerance to be tested. In practice it is possible to construct apparatus that will give results deviating by not more than 1/8 stop speed or 1/16 stop color balance when identical solutions are used for type and sample. This degree of reproducibility requires mechanical agitation, water baths for solution temperature control, and methods of quickly changing film from solution to solution. In the Ansco laboratory, an apparatus has been constructed employing a series of stainless-steel tubes each holding 1 1/2 liters of solution (Figs. 2 and 3). Special racks each holding two 35-mm strips in a film slide-type holder fit into the tubes. A rubber-edged vane, with a vertical movement operated by a series of pulleys over the tubes, is built into each rack. The whole unit is set into a water bath with temperature control. It is not necessary to employ exactly this design of apparatus, but mechanical agitation is strongly recommended.
Photographic solution control tests are interpreted by reading the color densities of the type and sample sensitometric strips on an Ansco color densitometer1 and comparing the plotted results for speed, density, and color-balance differences. Acceptable tolerances in processing solutions necessarily are high but specific acceptable limits must depend somewhat on circumstances. In general, solutions can be accepted that do not give speed differences greater than 1/4 stop or color-balance differences greater than 1/8 stop from type. Should an occasion arise where both the first developer and color developer or their respective replenishers show 1/8 stop color-balance difference, both in the same direction, the combination obviously would produce an intolerable result on the machine.
Normal machine-processing times are recommended for the solution control test machine except replenisher solutions are tested with two thirds the developing time of their basic solutions. It is desirable, although not absolutely necessary, that the solution control test machine and the processing machine turn out closely matched results. Often differences in agitation will make this difficult. The procedure for chemically adjusting color balance described in the section on machine adjustments would not be applicable in this case because it is necessary that the solution control machine operate to test the exact machine formulas.
2. Photographic Tests of Machine Operation
The basic purpose behind all preliminary testing is, of course, to control the actual developing machine. To this end the greatest reliance is placed on photographic controls because these indicate directly the results the machine is producing. Test strips are run through at 15- to 30-minute intervals. As the strips come off the machine, they are quickly compared visually with the preceding strips and the color densities of three representative toe, middletone, and shoulder steps read and plotted as shown in Fig. 4. The control chart that gradually accumulates as a result of plotting these continuous strips is of great value in controlling the machine. By connecting the points as the graph is constructed, a running record is obtained of the speed and color-balance fluctuations. Speed increases in reversible film are denoted by a drop in all layer densities, a speed decrease by a rise in all densities, while color-balance shifts are denoted by unequal changes in the various layer densities.
As can be seen from Fig. 4, minor fluctuations in over-all speed and very slight deviations in color balance occur between successive developments. These fluctuations are normal in the best regulated machines made to date and are caused by a variety of effects all minor in character but which add up to measurable differences.
The variables which cannot be absolutely controlled include slight differences in film emulsions, film exposures, chemicals, solution mixes, developing times and temperatures, circulation rates, drying conditions, and even final densitometry. These additive deviations may amount to as much as plus or minus ¼ stop speed variation as well as color-balance shifts of plus or minus 1/8 stop. It is the controlman’s responsibility to distinguish between a fluctuation that is within the optimum operating capability of his apparatus and a deviation that represents improper control. For this reason, graphical methods are employed. By following such a graph, it is possible to control the machine output within narrow limits. Fig. 5 illustrates another series of developments; it can be seen that for developments A through B fluctuations ranged upward and downward in a fairly regular pattern. This was normal machine operation. Beginning with B, although the fluctuations were still up and down, the majority was running higher than normal in density. This to the controlman indicated a definite trend toward lower speed that would require corrective measures. Since this rise was accompanied by a slight gain in the magenta and yellow density over the cyan layer in the middletone region (density 1.2) and also in the shoulder densities, he increased the replenishment rate of the first developer by 10 per cent. As can be seen by C’ to D (film C to C’ had passed through the first developer before the correction could be applied), this change of replenishment rate achieved the desired result as the speed increased and the color balance became more neutral.
In case of questionable deviations in the graph, complete sensitometric curves should be plotted for the strips involved. For general purposes, the three-step plot will suffice.
Many machine operators will prefer to run a pictorial type in addition to the sensitometric type since this gives them a clearer picture of the actual effect of machine differences on picture quality. The interpretation of pictorial strips should, of course, be given secondary emphasis as compared to the more accurate, numerical interpretation of the sensitometric control strips.
When deviations occur in the machine photographic tests, it is advisable to run a chemical analysis immediately to fix the cause of the deviation. Photographic side tests also may be made by using the solution control machine to compare a solution withdrawn from a machine tank with a type solution. Provided proper prechecking of solutions is made at the time of mixing, no serious deviations ever should occur. Such differences as do occur will normally arise from an excessive amount of high or low key film exposures, or from excessive aeration of solution due to leaky circulation pumps or from the aging of unused solutions.
C. Analytical Controls
The analysis procedure for the developer and bleach solutions are outlined in the paper by Brunner, Means, and Zappert.2 For routine machine operation, complete developer analysis should be run approximately every 48 hours. Bromide analysis of developers should be run every 4 to 8 hours as changes in bromide concentration are an accurate indication of improper replenishment rate. Bleach titrations should be run at 8-hour intervals. The condition of the bleach can be judged roughly by visually noting the time required for the bleach to etch out the silver antihalo layer. Bleach performance is generally satisfactory if this takes place in 1/3 the total bleaching time. It should never exceed 1/2 the total bleaching time.
The fixer tank should be analyzed for silver content at intervals of 8 hours of machine operation. Fixer performance is satisfactory if time of clearing does not exceed 1/2 total time of fixing.
II. Machine Control and Replenishment Data
Successful replenishment can be carried out on any type of equipment having fully controlled and reproducible temperature and agitation conditions. Within the Ansco plant, the system has been adopted to machines used for 16-mm film processing as described by Forrest,3 for 35-mm film processing as described by Harsh and Schadlich,4 and for rack-type sheet-film processing machines varying from a large Pako machine to small vane-agitated 3 1/2-gallon tanks. The value of replenishment is questionable for hand-agitation systems. The greatest control normally is obtained with the larger size machines that are in constant rather than intermittent use. It is desirable to maintain continuous filtration systems in both color and first-developer tanks as the build-up of gelatin particles, specks of oxidized developer, and other foreign material hasten the chemical breakdown of solutions. Proper filtration will keep both first developer and color developer clear and light in color after months of operation.
A. Modification of Processing Solutions to Change Color Balance
The widely varying agitation conditions existing in the different types of processing equipment introduce a complicating factor because variations in agitation can produce different color balances. Partial compensation for these balance differences can be obtained by increasing or decreasing developing times. However, in order to achieve the closest possible matches in speed, gradation, and color balance, it is sometimes necessary to make slight chemical changes in the processing solutions themselves.
The most convenient tools for modifying color-balance differences resulting from different agitation conditions are variations of the thiocyanate and iodide concentrations in the first developer solution. Chemical analysis of No. 502 first developer has shown that iodide accumulates during film development, and, depending somewhat on the type of film processed, exposure level and volume of replenisher added, normally reaches an equilibrium of from 3 to 6 milligrams per liter of developer. Iodide-analysis methods and a discussion of iodide equilibrium for black-and-white film developers were given by Evans, Hanson, and Glasoe.5, 6
Practical tests with color film show that even a small concentration of iodide exerts an appreciable restraining effect on the yellow and magenta layers giving an effective speed loss in these layers and a shift in the over-all color balance toward the brown. It can be shown that accumulation of iodide is responsible for a large part of the color-balance shifts that occur when a first developer is used. If small amounts of potassium iodide are added initially to the fresh developer, the color-balance changes are reduced. We have adopted the practice of adding small quantities of potassium iodide to fresh No. 502 first developer. No iodide is added to the replenisher solution.
Under processing conditions where only moderate agitation is encountered (as in Pako processing) bluish-cyan color balances are often encountered because the first developer is most active on the top layers of the film and does not easily penetrate to the bottom layer. Increased first development times under such conditions do not change the relative rates of development in the layers. However, the maintenance of a higher than normal iodide concentration will restrain first development in the top layers more than in the cyan layer and by use of slightly longer than normal developing times, a normal color balance can be achieved. In this case, it is necessary to maintain this high iodide concentration by adding a small amount to the replenisher solution.
The above color-balance shifts are essential for the processing of Types 234, 634, 235, and 635 sheet, roll, and 35-mm cartridge films since these materials must be balanced so they can be processed successfully both by amateurs with hand-processing outfits and by factory finishing. Obviously it is not necessary to achieve a so-called normal balance for a machine used to process a printing-type film whose balance is normally modified by printing filters, but it is of course essential that whatever balance is obtained be maintained consistently.
B. Replenishment Procedure
The following developer replenishes were worked out using the solution analysis technique described by Brunner, Means, and Zappert.2 Although the exact replenishment rates may require adjustment from time to time, use of the replenishes will maintain the solution ingredients very close to their initial concentrations.
Greater than 10 per cent variation in replenishment rates rarely are necessary. Trends that are not corrected by such changes eventually are traced to a mechanical or physical fault. Such difficulties should be solved by chemical analysis of the solutions in doubt. Through the knowledge of the film response to different chemical variations, skilled controlmen have maintained consistent color balances and speed over months of operation. The exact effects produced by photographic variations differ somewhat among different emulsions depending on the exact color balance of’ the emulsion. In general, variations of color developer affect the heavier densities to a greater degree than the lower densities whereas variations in first developer cause deviations in the over-all speed and balance of the film.
Relatively large quantities of replenishes are utilized in most cases. In the first developer, the rate is high to avoid build-up of bromide in the developer. In the color developer, replenishment rate is high because the replenisher solution is nearly as concentrated as possible. Bromide accumulates so slowly in the color developer it is necessary to add it in the replenisher solution to maintain the original amount. The short stop and hardener solutions are replenished at these high rates to prevent excessive accumulation of contaminants. No continuous replenishment is used with the bleach and fixing baths. The bleach is shifted to a separate tank, rejuvenated with bromine and after adding additional salts to make up for those lost by dilution, is returned to the machine tank. The fixer is used to exhaustion, then dumped into a large crock for sulfide recovery of silver.
2. Detailed Replenishment Procedure
The replenishment rates given in this paper are based on the rates used for the Ansco 16-mm and 35-mm developing machines. Other machines may perform best with slightly modified conditions or formulas. In fact, replenishment rates normally vary slightly during routine operation of any single machine. However, the formulas and rates of replenishment listed provide a close approximation of the requirements of any machine and are to be recommended as a starting point.
The developer replenishes were formulated using solution-analysis techniques and when used in combination with photographic and analysis tests have maintained developers over periods of months in the Ansco laboratories.
It is recommended that 3.5 to 5.0 milligrams per liter of potassium iodide be added to fresh tanks of No. 502 first developer. Analysis data indicate that the normal iodide-equilibrium ranges around these figures, subject somewhat to the exposure level of the film processed.
Changes in first developer activity are evidenced by over-all speed changes of the complete film. The exact color-balance differences obtained by increased or decreased amounts of first development vary slightly from film to film but generally increases of first development show up as reduced magenta density in the balance.
This solution is replenished at a rate necessary to maintain a pH of 5.0 to 5.5. The volume of replenisher is great enough to provide sufficient solution change to prevent accumulation of excessive developer solution. If the short stop pH is maintained at a higher pH than 5.5, increased hardening will result from the No. 901 hardener, but reduced short stopping action and scumming will be obtained. A pH lower than 5.0 produces less hardening by the No. 901 hardener and a pH lower than 4.5 may give difficulty with film blistering.
This solution is replenished with the same solution as the original at a rate necessary to keep the tank pH approximately 3.5 to 4.0. If the pH rises above 4.5 (although the hardening effect will increase up to a pH of about 5.0) chrome alum sludge and scum may also result. If the pH falls below 3.5, reduced hardening is obtained. Since a solution of chrome alum will hydrolyze on standing, the subsequent release of acid causes a natural drop of pH. The carry-over of a small quantity of alkali is not undesirable because it aids in maintaining the optimum pH.
Use of this replenisher, like the first developer replenisher, is designed to maintain the original concentration of developer ingredients. Regular bromide analysis will assist in maintaining the proper replenishment rate. No iodide is added to this bath. Analysis indicates some iodide is accumulated during use but the formula is relatively insensitive to this restrainer in the quantities involved.
It is recommended that No. 713 bleach be rejuvenated intermittently with bromine additions.
During normal bleaching operations, the bleach exhausts caused by depletion of ferricyanide and bromide ions as well as from dilution of the bleach solution by water carried into the tank by the wet film. The accumulation of ferrocyanide ions slows the rate of bleaching to a much greater extent than would be predicted from the depletion of ferricyanide. In practice, a concentration of potassium ferrocyanide greater than 5 grams per liter should be avoided. These concentrations can be detected using either the potentiometer method described by Brunner, Means, and Zappert2 or, if desired, the colorimetric method described by Varden and Seary.7
The ferrocyanide can then be reoxidized to ferricyanide by the direct addition of liquid bromine to the solution. This reaction produces bromide ions equivalent to the number of reoxidized ferricyanide ions and thus effectively regenerates the bleach bath. The chemical reactions of bleach exhaustion and rejuvenation are shown in Table VI.
It is recommended that a bleach bath be rejuvenated at intervals corresponding to 25 feet of 35 millimeters per liter of tank solution. This is conveniently done by providing two hard-rubber or ceramic mixing tanks for the bleach with pumps so that the solution may be pumped from the machine tank to either mixing tank for the rejuvenation treatment while machine operation is continued using the other tank of bleach solution.
A bleach exhaustion of 25 feet per liter normally corresponds to a potassium-ferrocyanide concentration of 4.5 to 5.0 grams per liter. With most technical grades of bromine, roughly 1.05 grams or 0.33 cubic centimeter per liter would be required to rejuvenate the bleach completely. In practice, however, in order to avoid the danger of adding an excess of bromine which would give excessive fuming and would be dangerously active both on the color film and on the tanks, spool banks, and so forth, it is desirable to retain a small amount of ferrocyanide in the bleach, normally 1.0 gram per liter or equivalent to the exhaustion produced by 5 feet of film per liter.
The addition of bromine should be made in a well-ventilated room or with a hood over the tank. Protective clothing and goggles should be worn as contact with the bromine will cause bad burns. The addition should be made slowly with vigorous stirring continued for a minimum of 30 minutes after the bromine addition is complete. The bromine will be assimilated more rapidly and with less fuming if it is first dissolved in 5 to 10 times its own volume of cold methanol and the mixture then added to the bleach mixing tank.
A second potentiometer titration should be made after the bromine addition to check the accuracy of the replenishment.
3. Replenishment of Diluted Bleach
The dilution of the bleach by the wet film can be corrected by making additions of the original chemicals in the same proportion as they were originally compounded. The degree of dilution can be detected by specific-gravity measurements using a hydrometer. No chemical additions are necessary unless the dilution exceeds 10 per cent. The specific gravity of fresh bleach No. 713 is approximately 1.110 at 20 degrees centigrade. Upon dilution, the specific gravity is reduced. An estimate of the degree can be made from the following calculation:
Table VII may be used as a guide for determining the required amounts of solid chemicals.
4. Fixing-Bath Control
No replenishment or rejuvenation is recommended for the No. 800 fixer. Electrolytic methods of silver recovery are difficult to apply to neutral or alkaline fixing baths. It is recommended that the No. 800 fixer be used until a silver concentration of about 2.5 grams per liter is reached or the time of clearing exceeds 1/2 the total available fixing time. When this point is reached, the fixer solution should be replaced by a fresh bath. The used solution may be treated with sulfides to recover the silver.
III. Summary of Testing Operations Recommended for Control of Color-Processing Laboratory
A. Testing of Raw Materials
The recommended raw material tests are tabulated in Table VIII. The frequency of tests will, of course, depend principally on the supply situation, size of shipments received, and number of manufacturer’s lot numbers involved. Emphasis should be placed on pretesting all lots of developing agents, sodium disulfite, and thiocyanate since variations in these chemicals are most likely to affect results. Less attention is required with the other chemicals once the consistency of a new source of supply has been ascertained. It is advisable to keep careful records of stock, date each chemical received, and date of its use for ready reference in tracking down variations in a solution mix.
A thorough pretesting policy will often prevent bad solution mixes and reduce the possibility of machine slowdown because of solution supply.
B. Testing of Solution Mixes
The recommended tests for solution mixes are shown in Table IX. Considerable attention should be paid to pretesting solution mixes before they are placed on the machine. Unless errors of solution mixing or of previously unobserved chemical differences are detected at this point, quality of machine output will suffer.
C. Testing During Machine Operation
The tests indicated in Table X should be made at consistent intervals to provide a constant flow of information to the machine control chemist.
In order to make correct decisions when photographic tests indicate trends away from normal, the control chemist should have at hand complete records of temperature and pH variations of all solutions as well as analysis of developers.
The authors wish to acknowledge with thanks the assistance of Mrs. A. Reed and Mr. J. Kowalak in this work. The co-operation of Mr. A. Brunner in supplying analytical data has been very helpful.
(1) M. H. Sweet, “Densitometry of modern reversible color film,” J. Soc. Mot. Pict. Eng., vol. 44, pp. 419–436; June, 1945.
(2) A. H. Brunner, Jr., P. B. Means, Jr., and R. H. Zappert, “Analysis of developers and bleach for Ansco color film,” J. Soc. Mot. Pict. Eng., this issue, pp. 25–36.
(3) J. L. Forrest, “Machine processing of 16-mm Ansco color film,” J. Soc. Mot. Pict. Eng., vol. 45, pp. 313–327; November, 1945.
(4) H. C. Harsh and K. Schadlich, “Laboratory for development work on color motion pictures,” J. Soc. Mot. Pict. Eng., this issue, pp. 50–58.
(5) R. M. Evans, W. T., Hanson, Jr., and P. K. Glasoe, “Iodide analysis in an MQ developer,” J. Soc. Mot. Pict. Eng., vol. 38, pp. 180–188; February, 1942.
(6) R. M. Evans, W. T. Hanson, Jr., and P. K. Glasoe, “Synthetic aged developers by analysis,” J. Soc. Mot. Pict. Eng., vol. 38, pp. 188–207; February, 1942.
(7) L. E. Varden and E. G. Seary, “Rapid test for ferricyanide bleach exhaustion,” J. Soc. Mot. Pict. Eng., vol. 47, pp. 450–453; December, 1946.
*Presented May 18, 1948, at the SMPE Convention in Santa Monica.”
(Bates, J. E.; Runyan, I. V. (1949): Processing Control Procedures for Ansco Color Film. In: Journal of the Society of Motion Picture and Television Engineers, 53,7, pp. 3–24.)
“Laboratory for Development Work on Color Motion Pictures
By H. C. HARSH and K. SCHADLICH
Ansco, Binghamton, New York
Summary – Precise control of all of the laboratory operations in producing color motion pictures is essential to obtain release prints of high quality. A description is given of a new building and equipment especially designed to carry on development work on all the laboratory phases of producing motion pictures in Ansco color.
Color-film materials for the professional motion picture industry have to meet a number of exacting requirements. In the case of multilayer color materials many of these properties have to be already
incorporated in the film. However, of equal importance is the proper processing of these materials and the requirements which are of particular importance can be summarized as follows:
1. Steadiness of the color image, free from processing fluctuations, streaks, and processing shimmer.
2. Methods for the preparation of dupes for optical effects, process photography, and protection masters.
3. Good sound reproduction.
In order to solve these well-recognized problems, a new laboratory was completed during 1948 which will be described briefly in this paper. Its facilities are used primarily to carry out development work on new and improved 35-mm color films and all aspects connected with the processing and use of these materials. The laboratory will provide technical assistance and data to commercial laboratories which are now processing and printing Ansco color films and serve as a source of information for those who are planning to set up a laboratory for this purpose.
The building, which is constructed of reinforced concrete and brick is 40 by 80 feet and is attached to a larger building which is now used as a finished goods warehouse but which is being converted entirely for research and development purposes.
Fig. 1 shows the plan of the first floor which includes two rooms for the processing machine, rooms for reeling, optical printing, release printing, sound testing, and editing as well as office space.
Fig. 2 shows the plan of the second floor which includes the solution-mixing room, control laboratory, air conditioning, office space, film vault, projection booth, and review room.
It was realized that the success of this pilot installation would be dependent to a great extent on the quality of processing which could be realized and the flexibility of the machine for experimental changes. In order to obtain a smooth screen quality every attempt has been made to provide the optimum developer turbulence conditions based on the available experience from the industry and consistent with other requirements.
The basic design is the same as the Ansco 4C 16-mm color machine described by Forrest.1 Substitution of 35-mm spools results in a lower machine speed of 30 feet per minute which for experimental purposes is quite adequate. The bottom-friction-drive principle, combined with an underdriving take-up spool, provides a smooth motion of the film through the machine which is very important for effective use of the high-pressure jet agitation system which will be described below.
The first section of the machine consists of the elevator and seven spool banks in four tanks. This section accommodates the first development, short stop, and hardening steps of reversal processing and when in operation is in no light. A lighttight pass box is provided between this room and the next which comprises the white-light section. In this section there are nineteen spool banks in twelve tanks which comprise the color development, short stop, hardening bleach, fixing and the several washing steps, followed by the drying cabinet.
Fig. 3 shows a side view of the white-light section of the machine with the spool banks partially raised. The wall on the west or operating side of the machine carries the control switches and recording instruments. The adjacent wall, near the pass box, partially visible in Fig. 3, supports the valves and flow meters which control the continuous replenishment of the developers, short stops, and hardeners.
An important new feature of this machine is the high-pressure jet turbulation which has been provided in both developers. A manifold coming into the top side of the tank supplies six jet tubes per spool bank. A cross-section schematic diagram of the jet arrangement on each bank is shown in Fig. 4. The jets are 3/16 inch from the film surface and opposite each jet tube are cloth-covered back-up rollers to support the film. It is important that the jets are regularly spaced and in this case the film passes a jet every 2 l/2 seconds. The jet orifice is 1 x 1/32inch. The two pumps have 7 1/2-horsepower motors which supply up to 12 pounds pressure at the jet and circulate the solution at the rate of 500 gallons per minute.
To the best of our knowledge, this is the first time that high-pressure jet turbulation has been used effectively on a bottom-friction-drive machine. As mentioned earlier, it is possible because of the uniform motion of the film.
The importance of adequate turbulence in processing color film can be demonstrated easily. For example, let us consider its effect in eliminating bromide drag. In Fig. 5 a type of sensitometric strip is shown which is designed to measure this effect quantitatively. The opposite circular areas receive equal exposures but in one case the immediate surrounding area receives maximum exposure and in the other the immediate surrounding area receives no exposure. The difference in the measured densities of the circular areas after processing gives a good quantitative evaluation of the efficiency of the processing in eliminating bromide drag. Fig. 6 shows sensitometric curves for the cyan layer of Ansco Color Type 735. The set of curves marked A were those obtained without using the jets and the dotted curve represents the exposures having the dark surrounding area. The second set of curves marked B shows the improvement obtained when only two jet tubes per spool bank at 10 pounds pressure are used. Finally, the set of curves marked C, with all the jets in use at 4 pounds pressure, are nearly coincident at all densities, which is the desired result for good screen quality. The effect in the magenta and yellow layers is similar although with inadequate agitation the difference is not so great as with the cyan layer. This result would be expected since the latter is at the bottom of the monopack.
Agitation is also used in the bleach, short stops, and fixer although the high pressure and frequency of jets as described for the developers is not necessary in these cases. Agitation of the short stops is very important for eliminating processing streaks and shimmer and in this installation the short stops are agitated by bubbling air through the tanks. For the bleach and fixer, single low-pressure jets without back-up rollers are located in the center of the tanks. For washing, nozzle sprays are used and have been found more efficient than full tanks.
The filters, jet and circulation pumps, air compressor, filter for the wash water, and other units are located in the basement under the machine.
The solution mixing room is located on the second floor directly above the front end of the machine. Seven stainless-steel mixing tanks, two small stoneware tanks, and a sink are located over this area with an operating platform in the center. The plumbing from these tanks to the machine is through black Seran pipe.
Six of the stainless-steel mixing tanks are used to supply the first developer, short stop, hardener, color developer, bleach, and fixer. The seventh tank is a spare connected to the color developer system. The two stoneware tanks are arranged so that they can supply solution to any machine tank through a utility line with flexible couplings.
By closing two valves the circulating pumps can be used to return the first developer, color developer, and bleach from the machine to their mixing tanks. This feature has proved expedient in experimental work and is convenient for maintenance and cleanup. In the case of the bleach, it is the most desirable procedure for carrying out the replenishment.
An exhaust system removes fumes from the color developer and bleach-mixing tanks.
The control laboratory, which is located next to the mixing room, is equipped to carry out the control procedures and chemical analyses described in the papers by Bates and Runyan2 and Brunner, Means, and Zappert.3
Standard equipment with slight modification is used for optical and release printing. An Acme optical printer is used for printing masked duplicates and special effects. The basic features of this printer have been described by Dunn.4 A Bell and Howell Model D, modified with an optical system for increased illumination and with a filter-change devise for scene-to-scene correction, is used for printing.
The equipment for sound testing, which has not yet been installed, will include complete channels for recording and re-recording variable-area and variable-density tracks and the necessary accessory instruments for measurements.
The projector is a standard Super-Simplex E7. Because of the relatively short throw, wire screens are used in the light beam to reduce the screen brightness to 10 1/2 foot-lamberts.
A photograph taken from the front of the review room is shown in Fig. 7. For the acoustical treatment of the walls and ceiling, perforated panels of Johns-Manville gray Transite backed up with rock wool are arranged appropriately with unperforated panels of the same material. The floor is carpeted to within 11 feet of the screen. Live sections in the front of the room are provided in order to give the optimum results at the rear three rows of seats. Measurement of the reverberation time as a check on the efficiency of the design gave results very close to the desired theoretical values.
1 J. L. Forrest, “Machine processing of 16-mm Ansco color film,” J. Soc. Mot. Pict. Eng., vol. 45, pp. 313–327; November, 1945.
2 J. E. Bates and I. V. Runyan, “Processing control procedures for Ansco color film,” J. Soc. Mot. Pict. Eng., this issue, pp. 3–25.
3 A. H. Brunner, Jr., P. B. Means, Jr., and R. H. Zappert, “Analysis of developers and bleach for Ansco color film,” J. Soc. Mot. Pict. Eng., this issue, pp. 25–36.
4 L. S. Dunn, “The new Acme-Dunn optical printer,” J. Soc. Mot. Pict. Eng., vol. 42, pp. 204–211; April, 1944.
Presented May 18,1948, at the SMPE Convention in Santa Monica.”
(Harsh, H. C.; Schadlich, Karl (1949): Laboratory for Development Work on Color Motion Pictures. In: Journal of the Society of Motion Picture and Television Engineers, 53,7, pp. 50–57.)
“THE DENSITOMETRY OF MODERN REVERSIBLE COLOR FILM*
MONROE H. SWEET**
Modern Reversible Color Film. – In the past few years, manufacturers of photographic products have developed reversible color films which yield positive transparent images capable of reproducing practically the entire gamut of colors found in everyday life.1,2 These materials are called multilayer color films and, after processing, form 3 superimposed dye images. The dyes used are cyan (minus red), magenta (minus green), and yellow (minus blue). To maintain control of product quality and to determine, quantitatively, the effect of different illumination and processing conditions, routine sensitometric tests are conducted in a manner which is especially adapted for evaluating the photographic characteristics of color materials. This paper is chiefly concerned with the densitometry of the processed sensitometric strips.
General Sensitometric Technique for Reversible Color Film. – In black-and-white photography the measurement of the speed, gradation, and fog of the emulsion is the principal object of ordinary sensitometric studies but the accuracy demanded is relatively low and for practical use speeds may be figured in half stops. Reversible color film, on the other hand, necessitates much closer control of the sensitometric variables – lighting, exposure, and development – than black and white and, since the original image is the one intended for viewing, ordinarily no correction is afforded through printing.
Color sensitometry, like black and white, may be classified in 4 steps:
(3) Density evaluation.
(4) Interpretation of results.
In the Ansco Color Laboratories, routine tests of production samples of Ansco Color Film are made by exposing strips on an intensity-scale sensitometer whose source-filter combination has been adjusted to duplicate practice. Processing is, of course, rigidly controlled to conform with standardized techniques. The processed sensitometer strips are analyzed on a special photoelectric densitometer adapted to read color densities in 3 spectral regions and these results may be used directly, or they may be converted into equivalent densities. By comparing the color density versus log E curves with similar curves for materials known to give optimum results in practice, it is possible to determine what adjustment, if any, should be made in the final product for best color rendition.
Color sensitometry has been discussed in the literature in greater detail than that warranted in this paper and the reader is directed to the references for discussions of the many factors involved.
General Aspects of Density Measurement. – In general, optical density is defined as the common logarithm of the reciprocal of the transmission, D = log10 1/T. However, for practical specimens the numerical result will vary according to the mode of illumination and collection (the geometry of the system) and also according to the spectral character of the light source, specimen, and receiver. For most black-and-white photographic work wherein prints are to be made from negatives, experience has shown that diffuse printing density is suitable as a reference standard.3
The densitometry of reversible color film, on the other hand, is somewhat more complex owing chiefly to the spectral character of the specimen. Given a color film patch of uniform color the problem arises of how to define the density of the pack as a whole and of each layer separately from the spectral standpoint. Fig. 1 shows the density versus wavelength relationship for each layer of a sample which appears gray under ordinary viewing conditions. Also shown is a curve representing the integral spectral densitya of the 3 layers.
It will be noted that the magenta and cyan layers contribute significant amounts of blue density although they are nominally transparent in this region of the spectrum. For specimens which are visually grayb it is appropriate to use simply visual density (with an incandescent light source) as the criterion of absorption in the reversible process. However, for off-gray samples the concept of visual density is difficult to apply and, therefore, the characteristics of the 3 layers have to be expressed separately. Heymer and Sundhoff4 proposed “grauaequivalente Farbdichte” (gray equivalent color density) which Evans5 called simply “equivalent density” and defined as the visual gray density of a single layer of an off-gray sample to which sufficient density of the two other layers of the process is added or subtracted so as to produce a visual gray result. Thus the gray specimen whose spectral characteristics are represented in Fig. 1 has equivalent densities of 2.5 for all 3 layers. In Fig. 2 a specimen deficient in its cyan dye is shown. This specimen has the same equivalent densities for its magenta and yellow layers as that shown in Fig. 1. The equivalent density of the cyan layer, however, is only 2.2, for when sufficient density is subtracted from the magenta and yellow layers to give a gray result (as represented by the broken lines) the visual gray density of the pack is found to be 2.2. It will be observed that
(1) Because of “spectral impurities” in practical color film dyes the equivalent density of a given layer of a given sample will always be considerably higher than its maximum spectral density. (This statement would not apply to processes wherein the dyes were ideal and were mutually complementary.)
(2) The ratio between the spectral densities of any 2 dye images at any wavelength is constant when the dyes are present in such concentrations as to produce gray.
Evans has shown that by constructing a visual densitometer in which controllable amounts of the 3 dyes may be introduced into the photometric beam the equivalent density of each layer may be evaluated. It will be apparent that if in off-gray samples the exact amounts of the complementary dyes necessary to produce gray were known, the equivalent densities can be evaluated directly. (See Fig. 2.) In this way, Sensitometer strips in which the 3 dyes are always present can be evaluated, layer by layer, as though the 2 complementary layers were not present, and the behavior of the individual layers can be studied. The 3 sets of equivalent density values can be plotted against log E and the results checked against those obtained for samples known to be in satisfactory color balance.
Fig. 3 shows the equivalent density versus log E curves for a sample having a magenta-colored maximum density, gray middle tones, and a yellow toe. A sample which faithfully reproduces gray at all density levels will, by definition, have identical equivalent density versus log E curves for all 3 layers. However, it should not be inferred that emulsions which faithfully reproduce gray are necessarily superior in all respects to others which do not. Gradation, color contrast, saturation, and other factors are also involved.
R. Bingham and H. Hoerlin, of this laboratory, have shownc that it is possible to evaluate a specimen in terms of its equivalent densities from the integral spectral densities measured at 3 different wavelengths, if the ratios of the densities of the dye components at each of the wavelengths are known. It can be readily understood that for every different combination of densities of the 3 dyes there will be a unique set of 3 integral density readings and a corresponding set of equivalent density values. Those familiar with masking processes may grasp the principles involved, in fact, the 3 equations (all linear) which show the relationship between the equivalent density and the integral density readings are identical with those used in connection with the automatic masking technique in subtractive color processes and have been given in the literature.6
Integral density readings made at the 3 wavelengths corresponding to the maximum absorption of the dyes also give useful information directly and can be interpreted to some extent without resort to supplementary computation. This is particularly true after some experience is gained in analysis of these values. By direct comparison of curves plotted from the density readings for a test specimen with similar curves for samples known to be in perfect color balance, qualitative interpretation of the results is possible. The comparison of these curves is further facilitated if the 3 wavelengths chosen for the measurements are such that the integral spectral densities are equal for gray specimens. Then the three D versus log E curves will be superimposed for strips which are in perfect color balance.
Figs. 3 and 4 show a comparison between equivalent density and densitometer (integral) density versus log E values for one and the same off-balance sample.
General Requirements of a Color Densitometer. – From the above discussion it is apparent that a satisfactory method for density evaluation is important in cases where large numbers of Sensitometer strips are handled. In contemplating the general requirements for a suitable color densitometer the following comments are pertinent:
(1) The instrument should be objective and direct reading. This not only eliminates visual fatigue and error, but also introduces the possibility of attaching a recorder where such is warranted.
(2) For simplicity of design the instrument should read the integral spectral density of the specimen at each of the 3 wavelengths. Although it would be desirable in many respects to design the instrument to read equivalent densities, directly or by a null point balance arrangement (the photoelectric counterpart of Evans’ densitometer), a number of inherent design complications and phototube deficiencies made it advisable to choose the simpler direct-reading color densitometer which gives the integral density values at 3 wavelengths at or near the absorption maxima of the 3 dyes of the process.
(3) The density range should be at least 0–3 for all colors.
(4) Spectral purity of the optical components of the densitometer should be commensurate with the character of the dyes to be analyzed. If the “monochromatic” filters have too broad a wavelength transmission band, the effective sensitivity of the instrument to small differences in the concentrations of the dye images will be reduced, and it will also make the subsequent calculation of equivalent density values inaccurate or extremely complex.
(5) Many other obvious factors such as stability, reproducibility, speed of response, etc., should fall within satisfactory limits. Most of these factors are common to black-and-white densitometers and have been discussed in the literature.7
Suitability of Existing Densitometers. – After it was agreed that a densitometer of the type indicated by the above requirements was needed, the possibility of using a previously developed black-and-white instrument was examined. A simple direct-reading photoelectric instrument had been designed and proved reliable,7 and it seemed possible to modify this instrument for reading color densities. The commercial model of the instrument is shown in Fig. 5. Fig. 6 is a phantom view of the operating components. Light from a 15-cp automobile headlamp is focused on a small aperture and collected by a phototube. The phototube current is fed into the grid circuit of a triode and the plate current is measured directly on a 1.0-ma d-c output meter. A circuit diagram is shown in Fig. 7. Because the relationship between grid current and plate current is logarithmic, the output meter response is uniform for uniform changes in the density of the specimen over a wide range of density values.
In its commercial form this instrument is too insensitive to meet requirements (3) and (4) simultaneously. Furthermore, it is not provided with filter holders for easy and rapid interchange of filter sets. By replacing the 15-cp light source with a projection lamp of higher candlepower and collecting a greater solid angle of flux, fairly pure monochromatic filters may be used, and a density range of 0–3 can still be covered.8 However, the deficiency in relative red sensitivity of the type S–4 photosurface used in the instrument is just enough to necessitate resort to a more sensitive amplifier circuit because a spectrally pure red filter reading is required for the present application.
The electrostatically focused electron multiplier phototube9 provides a receiver having a net photosensitivity of the order of 104 times as great as that for the common type of phototube used in the commercial instrument.
A representative 9-stage multiplier phototube is the type 931, illustrated diagrammatically in Fig. 8. Light striking the photocathode liberates electrons. Assuming one electron to be liberated by the action of the light on the photosurface, it is attracted to the first dynode – a cup-shaped plate held at a positive potential with respect to the photosurface. When the electron strikes the dynode two or more secondary electrons are released. These electrons are attracted to a second dynode which is held at a still higher positive potential. The multiplying action is accomplished in this manner and in 9 dynode stages the amplification factor may be made as high as 200,000. However, direct coupling of such a tube to the high impedance grid circuit of the logarithmic amplifier used in the original densitometer presented some difficulties, principally because polarity relationships demand that the entire power supply must be connected to the 6F5 grid and must also be shielded and insulated to an extent which is comparable in impedance with the (1000 megohm) grid bias resistor. Obviously, no ordinary a-c supplied power pack would meet these requirements. Furthermore, stability of the output voltage would be entirely inadequate unless special circuit precautions were observed.
By connecting 10 miniature 67 1/2-v batteries in series, a compact power supply is obtained which provides the necessary number of voltage taps as well as the high (700 v) voltage necessary for efficient operation of the multiplier tube. The entire pack measures only 4 x 5 x 7 in. With this pack it is relatively easy to meet the shielding and insulation requirements demanded by coupling to the basic grid circuit. The voltage stability of the battery pack is far better than that required, largely because the current drain is infinitesimal for all except the last stage. The last stage operates at 30 μa maximum current (at zero density), and even this current is negligible in comparison with the load for which the battery was designed. When used in this manner the life of the pack is therefore equal to the shelf life of the batteries and with continuous daily use a given set of batteries will serve for well over a year before the terminal voltage drops prohibitively.
However, 3 troublesome factors accompany the use of the multiplier phototube in this application:
(1) The dark current of the majority of commercial multiplier phototubes is appreciable in terms of the operation of the triode amplifier stage. Since a density range of 0–3 is to be covered, this means that the ratio of multiplier tube output currents must cover a range of 1000 to 1. Since it is difficult to operate small triodes in the desired logarithmic manner at grid currents in excess of 50 μa, and since the red sensitivity of available multiplier phototubes is low (and the maximum output for the red filter readings will be correspondingly low), the grid current for a density reading of 3.0 will be of the order of magnitude of 0.05 μa and dark currents greater than about 0.01 μa cannot be tolerated. Difficulties owing to excessive dark current may be avoided by careful selection of multiplier phototubes.
(2) At this writing there are no multiplier phototubes commercially available in photosurfaces which have high sensitivity throughout the visible spectrum.
The best compromise was found to be the type 931 tube which has a caesium-antimony (S–4) surface characterized by high blue-green sensitivity and relatively very low red sensitivity. As a result it is necessary to alter the optical system in order to obtain the maximum possible red energy for the red filter reading. There is a very large individual variation in the far red sensitivity of photoelements having a caesium-antimony photosurface and by choosing a tube which not only has low dark current but also high red sensitivity the second difficulty may be minimized.
(3) The high gain associated with the multiplier tube, together with the extensive physical area of elements (battery pack and multiplier tube leads) connected in the triode grid circuit forms a system which has a strong tendency to oscillate, particularly at low levels of illumination wherein the net grid-ground impedance is high. Oscillation may be avoided by proper shielding alone, although it is also helpful to insert a grid bias by-pass condenser of about 0.001 μf to act as a suppressor. (Higher capacitance values would cause sluggish meter response at high density levels wherein the grid to cathode d-c impedance is high.) No additional changes in the circuit were necessary. A wiring diagram of the complete circuit is shown in Fig. 9.
A 50-cp lamp energized by a separate stabilizer and low voltage transformer served as the light source. A filter disk holding 3 sets of gelatin filters was mounted on a shaft. The shaft of an electrical tap switch was coupled with the filter disk in such a manner that as each filter was brought into the beam, a different variable resistor was connected in series with the primary of the light-source transformer so that once all 3 resistors are properly set changing from filter to filter will not necessitate readjustment of the zero setting. This has the additional advantage of preventing accidental overload of the grid circuit. By using fixed resistors in series with the rheostats, it becomes possible to effect a relatively fine adjustment of the zero setting and also to avoid the possibility of accidentally closing the lamp circuit completely and thereby increasing the lamp intensity beyond safe limits. A pictorial diagram of the optical control system is given in Fig. 10.
The selection of the blue and green filters was not difficult. The high sensitivity of the instrument in these spectral regions permitted the use of dense color filters in order to obtain sharp cutting monochromats which have their peak transmission at the desired wavelengths. It was found that Wratten filters 36, 2A, and 38A used in combination were satisfactory for the blue, and Wratten 62 and 16 for the green. Their density-wavelength curves are illustrated in Fig. 11.
The selection of filters for the red reading presented a problem. This is partly because no efficient sharp cutting infrared absorber with a cutoff at about 660 mμ is available. The best compromise was found to be the cupric chloride solution used in the maximum concentration tolerable in view of the light intensity available and the sensitivity of the photoelectronic system. A Wratten 70 and 16 filter combination was used to absorb the short wavelength radiation for this reading. It was found that the temperature coefficient of spectral density of the cupric chloride filter was very high – so high, in fact, that it changed the spectral purity of the red readings by a significant amount when heated only 10 C above room temperature. By inserting a Jena BG19 heat-absorbing filter between the light source and the cupric chloride solution this effect is minimized.
Fig. 12 shows the interior of the instrument case. The case itself is electrostatically shielded and contains the battery pack (in an additional shield), light-source control resistors, and the optical system. The standard power pack for the logarithmic amplifier is mounted on the rear of the case and a separate voltage stabilizer for the light source is mounted on the other side.
Fig. 13 shows the instrument in routine use. The control knob at the right-hand side of the output meter is used to rotate the filter disk and insert the proper resistors in the light-source control circuit.
Calibration. – It has been found experimentally that the photocurrent response as a function of illumination of the type S–4 photosurface is nearly linear over a wide range of flux density levels and is not altered significantly for radiation at different wavelengths. The instrument was therefore calibrated, empirically, using the blue filter readings of a standard photographic silver wedge.
Performance. – From an over-all standpoint, the instrument performed satisfactorily in routine daily use. The zero reading stability was within acceptable limits although the inherent fatigue effects of the present-day multiplier phototubes are detectable when a dense sample is measured immediately following the measurement of a sample of very low density.
The day-to-day reproducibility is satisfactory as may be seen from Fig. 14. In this figure, readings were taken daily at different density levels for a given wedge over a period of one (typical) month.
The instrument is checked periodically for the spectral purity of its density values by measuring the blue density of a yellow filter, the green density of a magenta filter, and the red density of an infrared transmitting filter. If any of these readings depart significantly from their norm, in the presence of a satisfactory black-and-white calibration, this indicates that the net spectral response of the system has shifted. However, since little ultraviolet, and no infrared radiation reaches the gelatin filter sets, it is expected that this effect will not be a source of difficulty.
High-Density Measurement. – Aside from its application as a color densitometer the instrument has been found useful in the measurement of high densities of ordinary black-and-white materials. This is done by eliminating color filters from the optical system and using a momentary-close push button switch which inserts a low resistance shunt across the normal black-and-white resistor shown in Fig. 10. When properly adjusted, a specimen of density 3.0 will read 0.0 with the switch depressed and a specimen of density 6.0 will read 3.0. By increasing the lamp voltage still further, the instrument can be used to read densities up to 7.3. The sensitivity of the instrument to luminous flux is such that a density reading of 3.0 corresponds to 0.01 microlumen.
1Forrest, J. L., and Wing, F. M.: “The New Agfacolor Process,” J. Soc. Mot. Pict. Eng., XXIX, 3 (Sept., 1937), p. 248.
2 Mannes, L. D., and Godowsky, L., Jr.: “The Kodachrome Process for Amateur Cinematography in Natural Colors,” J. Soc. Mot. Pict. Eng., XXV, 1 (July, 1935), p. 65.
3 Sweet, M. H.: “An Improved Procedure for the Contact Printing Method of Measuring Photographic Density,” J. Opt. Soc. Am., 33, 3 (Mar., 1943), p. 143.
4 Heymer, G., and Sundhoff, D.: “Measurement of the Gradation of Color Film,” Veröffen. wiss. Zentral-Lab. phot. Abt. Agfa, 5 (1937), p. 62.
5 Evans, R. M.: “A Color Densitometer for Subtractive Processes,” J. Soc. Mot. Pict. Eng., XXXI, 2 (Aug., 1938). p. 194.
6 Miller, C. W.: “Principles of Photographic Reproduction,” Macmillan Co. (New York), 1942, ch. 25, p. 313.
7 Sweet, M. H.: “A Precision Direct-Reading Densitometer,” J. Soc. Mot. Pict. Eng., XXXVIII, 2 (Feb., 1942), p. 148.
8 Sweet, M. H.: “The Spectral Characteristics of Optical Wedges,” J. Opt.
Soc. Am., 33, 4 (Apr., 1943), p. 194.
9 Rajchman, A., and Snyder, R.: “An Electrically Focused Multiplier Phototube,” Electronics, 13, 12 (Dec., 1940), p. 20.
a By “integral spectral density” we mean the total density of the 3-layer specimen at the wavelength in question.
b A distinction should be made between the terms “gray” and “neutral.” A “neutral specimen” is one which is completely nonselective in its spectral absorption characteristics. A “gray specimen” is one which gives the same visual impression as that of a neutral sample.
c Private communications – to be published.
* Presented Oct. 17, 1944, at the Technical Conference in New York.
** Research Laboratories, Ansco, Binghamton, N. Y.”
(Sweet, Monroe H. (1945): The Densitometry of Modern Reversible Color Film. In: Journal of the Society of Motion Picture Engineers, 44,6, pp. 419–435.)
“Ansco Color film was made generally available to the public, and in 1945 three types of Professional 35mm. Ansco Reversible Film were announced, including a duplicating film and positive film for release prints. Special processing machinery has been constructed, and machinery has been installed in commercial laboratories.
The range and accuracy of colour reproduction is excellent, although somewhat lacking in saturated reds due to the magenta coupler yielding a somewhat desaturated hue. All types so far available are designed for reversal processing. First and second generation dupes, of fair quality, have been made.
This process is an important addition to the choice of colour films available to the motion picture industry.
Nitrate or Cellulose Acetate safety film base coated with three emulsion layers (excluding a yellow filter layer of colloidal silver and the anti-halation coating) selectively sensitized to three spectral regions, red, green and blue. The outermost emulsion is blue sensitive, next comes an interlayer of colloidal silver comprising a yellow filter to prevent further penetration of blue light, the middle emulsion is green sensitized, the bottom emulsion is red sensitized and with little or no green sensitivity. The base is coated with an anti-halation backing of colloidal silver beneath the bottom layer of emulsion (Fig. 212 A).
The colour couplers are subtractive to the gelatin emulsions in which they are dispersed, their non-diffusion characteristic being achieved by the addition to the couplers of long chain fatty acids. Similarly the sensitizers are non-diffusing.
The camera film is sensitized without a break through the visible spectrum, the maximum sensitivity being at 650 Mμ, 550 Mμ and 400 Mμ. The positive has sharp sensitivity peaks and a complete break at 575 Mμ. The red sensitivity is continued much further into the red than with the camera film, the maximum being at 680 Mμ.
Ansco Color Type 735 is softer in gradation compared to regular Ansco Color Film, the grain is finer and the colour balance purposely set off-natural.
Ansco Color Camera Film is available on both nitrate and acetate film base and designated 735 and 835 respectively. The former is balanced for exposure in bright sunlight; or for studio exposures, the key-light should be provided by H.I. carbon arcs modified by Y-1 gelatine filters and fill-light by tungsten lamps (3,200° K.) filtered with Macbeth Whiterlite glass. The spectrogram shown in Fig. 214 gives the relative response of the film to the visible region of a daylight spectrum.
For optimum print results the film should be slightly underexposed or somewhat heavier in density than is the normal practice when exposing for screen projection of an original, in order to maintain as much of the exposure as possible on the straight-line portion of the characteristic curve and avoid inaccurate colour reproduction from exposures failing in the region of the toe. This film should be processed for a somewhat shorter time in both first and colour developer than in the times given for 16mm. processing.”
(Cornwell-Clyne, Adrian (1951): Colour Cinematography. London: Chapman & Hall, 3rd. ed., on pp. 390–392.)