This type of sensitizing is typical of most monopacks, such as Kodachrome, Kodacolor, Ektachrome, and Ansco Color film. The ideal sensitivities can be mathematically calculated relative to either practical or theoretical synthesis, by additive or subtractive methods but the best compromise has to be effected with the materials available Fig. Since it is desirable that the positive material should record in each of its respective layers light modulated by only one layer of the negative, the sensitizing should be designed to correspond to the maximum absorption and minimum overlap of the spectral transmission of the negative dyes Fig.
The relation between negative colours and positive sensitizings can in fact be such as to overlook any relation whatever to what we might expect to be the normal appearance of colours in the negative.
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By this is meant that the negative colours need not be complementary to the colour of the light recorded. See below. The negative cyan coupler in the present product has remarkable absorption in the deep red and by placing the red sensitivity of the positive far into the red we are assured of the cyan layer of the negative being efficient to modulate this layer only Fig.
Thus the relation between negative and positive can be expressed as follows:. Schneider and others have suggested that there is no reason theoretically why a positive material should not be sensitized, say, in the infra-red, green, and ultra-violet regions, respectively, in order to obtain a more complete colour separation Fig.
In this case the absorption maxima of the three dyes present in the layers of the negative would also have to be in the infra-red, green and ultra-violet Fig. A dye that absorbs only in the infra-red or in the ultraviolet would be colourless to the dye. Such negative material would be magenta only. The development of Agfacolor negative or positive film requires only minor modifications of the standard machines.
We have to provide for a bleaching bath and for washing for a more prolonged period than usual. It is recommended that washing should be entirely carried out by fine jets, or better still by the use of a flat jet issuing from an inclined flattened nozzle. Afterwards the solution is again brought to the prescribed working temperature,. The simplest layout consists in inserting this apparatus in the developer circuit, otherwise the developer must be strongly agitated to ensure uniform development.
Plastic materials have been found satisfactory for pumps, and in general, plastics have stood up well for piping and tanks. Precautions must be taken to prevent the formation of foam in circulated solutions to avoid rapid ageing of baths by oxidation.
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Subsequent to development the washing must be very thorough otherwise a general blue fog will be formed in the bleaching bath if the washing is inadequate. It is absolutely essential that hypo should be completely removed in the final wash. Tanks and tubes have been entirely abandoned for washing at any stage. Figs, and show the type of spray wash recommended.
Subsequent to the first spray wash, or in any case after the bleaching bath the remainder of the processing can be carried out in ordinary illumination.
The explanation of the inclusion of a stop bath in the positive sequences is that there is some advantage to be gained from the fact that the developer remaining in the layers continues to be active during the washing, but whereas the developer is soon exhausted in the fully exposed areas the shadows still retain a sufficient supply of fresh developer which continues to produce silver and dye images.
The resulting slight fog is of no consequence in the case of the negative film. In the positive film the highlights must be free from fog, and so the action of the colour developer must be interrupted immediately after development. For this purpose acid salt solutions are suitable, for in spite of the permanent addition of alkaline colour developing solution they retain their hydrogen ion concentration at a p H value of 4 to 5, for some time. At the same time, by virtue of the formation of easily dissolved salts the developing agent is washed off more quickly.
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It should be noted that when a silver sound track is desired it is necessary to use an additional and preliminary weak bleach to eliminate the colloidal silver yellow filter layer before applying the final viscous bleach on the picture area see below. This can be done with a weak bleach which is not strong enough to affect any of the silver in the sound track image. Furthermore it is desirable to include a brief immersion in a five percent, solution of sodium sulphite immediately after the final bleach, to inhibit its action before it has a chance to flow over on to the sound track during the spray wash which succeeds the bleaching bath.
The bleach bath is a preparatory stage in the removal of the developed metallic silver entirely from the dye image. Having formed a silver salt, such as silver ferrocyanide, it is easily eliminated by the solvent action of hyposulphite. Simultaneously the unexposed silver halide is eliminated. The conventional photocells in use in most projector sound reproducing systems are of the type using a sensitive coating of caesium—silver—oxygen, which is mainly sensitive to red and infra-red radiation.
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The dyes used in colour development processes transmit radiation in this region, with the result that a dye track is unsatisfactory when used in conjunction with a large proportion of the phototubes used today. While new photocells have been recently developed having high sensitivity in the green-blue and blue regions of the spectrum, and with these dye tracks are capable of reproduction equalling in quality that of silver tracks, it is nevertheless desirable for the time being to continue to employ the silver image sound track. The German solution of this problem was ingenious.
Obviously the silver track must not be bleached if it is to be retained. The bleaching agent, potassium ferrocyanide, is therefore mixed with a suitably viscous agent and coated only on the picture area of the film. The bleaching solution see formula below is applied to the film from beneath, using a nozzle. This nozzle is supported in such a manner that any join, or film clips, will not jam.
There is the obvious advantage of using film travel in the vertical direction for the bleaching stage, and thus saving laboratory floor space. The yellow colloidal silver layer is destroyed in the bleaching bath and it follows therefore that it will remain in the sound track. Its presence has been found to be of no consequence provided that the present red sensitive photocells are employed. Should the sound track, however, be intended for use with the new caesium- antimony blue sensitive photocells it is necessary to destroy the colloidal silver yellow layer by the use of a weak bleaching agent which has no effect upon the silver of the sound track image.
Subsequently the final viscous bleach may be employed to remove the silver in the picture area as we have described. Very rigid control was instituted in the Continental laboratories which processed Agfacolor negative-positive motion picture film. At the Afifa laboratory in Berlin the developer from the time of preparation was analysed and corrected if necessary. After 24 hours rest a new analysis indicated whether there was cause for further correction.
The bath was analysed twice a day. The hydroxylamine content is measured volumetrically by oxidation with potassium ferrocyanide. The viscous bleach is applied to the picture area only and is used when a silver sound track is desired. Surface squeegeeing methods have also been employed to remove the bleach before washing.
Normal contact or optical printers may be employed; all existing apparatus is therefore usable, but minor modifications must be incorporated in order to make provision for colour grading. In all colour processes in which the print is made in one operation from a coloured negative there must inevitably be two factors to control:. The first factor is controlled by the intensity of the printing light as in printing black-and-white.
The second factor is controlled by varying the distribution of energy in the spectrum of the printing illuminant. It is the second factor which necessitates the introduction of additions to existing apparatus, since the most convenient means of modifying the spectral character of the light is by the automatic introduction of minus red, minus green and minus blue filters into the illumination system. The introduction of a minus filter may obviously reduce the total energy of the printing light and therefore have an effect upon the general density of the print.
Hence in printing colour films such as Dufaycolor or Agfacolor the two factors are interrelated. In general it is impracticable to control the light energy by the introduction of a resistance in the lamp circuit since this alters the temperature of the filament with important effects upon the distribution of energy radiated.
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The effect of this will be tantamount to the introduction of a colour filter and the results will be too complex to predict with accuracy. It is essential accordingly to keep the voltage over the lamp fixed within severe limits and to use filters only for altering the volume of light in different regions of the spectrum. The minus filters should have absorption curves closely similar if not identical to the dyes used in the layers of the positive film, thus there can be established a simple relation between the dyes used in the negative film and those of the filters, i.
The filters may be used in combination, each filter reducing the exposure of a certain layer of the positive.
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The colours of the filters will then have the same meaning or sign. Thus a yellow filter corrects a yellow hue, and a blue filter, composed of a cyan and a magenta, corrects a blue hue. The range of filter densities was determined by the following method: a yellow, a magenta and a cyan filter are combined and the light source identical to the printing source viewed through the combination.
The respective densities of the filters are altered until a neutral grey is obtained having a density of The three filters so determined are arbitrarily assigned a value of The values of all the other filters are decimal fractions of the calibration filters.
Six figures are employed. The first two designate the concentration of the yellow filter, the middle two that of the magenta filter, and the last two figures refer to the cyan filter. For example, 30 90 means: no yellow filter, a 30 per cent magenta filter and a 90 per cent, cyan filter. These figures can be added or subtracted. When changing over to a new positive batch, the filter value of this material has to be subtracted, for example:.
source Usually 10 steps of each filter colour are ample, but occasionally 5 per cent, steps are used. Thus 30 filters comprise a complete set. A set of filters of the values 10, 20, 30 and 50 would yield every possible combination. The Continental laboratories made use of the well-known Debrie diaphragm strip. In this machine the volume of fight is controlled by means of circular holes in a paper strip. The filter foils are attached over the holes with light metal clips. The size of hole controls the total fight volume or a neutral grey may be added to the colour filter Fig.
In practical printing filter numbers for each scene must be ascertained by direct testing.
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Experience showed that with a single frame light change covering every combination, the most satisfactory grading system was to provide a ribbon control carrying not only a series of diaphragm widths but also all combinations of the filter numbers 30, 60 and 90 consisting of 47 frames for ten diaphragm steps:.
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