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:. 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.
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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. 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:. From the developed test print, the most neutral frame can be selected with ease, and from the diaphragm series the optimum printing fight can be determined.
Next on a fine control ribbon all combinations are recorded in ten steps centred on the most neutral setting. For a rough filter value of 60 60 00 these values are:.
The writer is unaware of whether or not it is the practice to correct the colour balance of a motion picture print by a subsequent bath intended to reduce one of the three subtractive primaries. If the excess is red, green or blue, then baths must be successively used of yellow and magenta reducers, cyan and yellow, or magenta and cyan. Apparently two filters are occasionally employed for a brief period should operation demand it.
For direct illumination Agfa No.
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The latter position was selected for the maximum transmission of the safelight filter, owing to high sensitivity of the retina in this region, and resolving power is also higher than for red or green light. It is better to have high visual acuity in the darkroom than high illumination. While filters can be made which transmit light of a narrow wavelength band in the yellow region they are not efficient. These safelights must be mechanically air-cooled. Using two filters of 20 x 30 cm.
The safety margin for Agfacolor positive is 30 minutes. The German technicians do not seem to have used a special illuminant in printing machines. A system of combination of light sources such as has been successfully used for the printing of Dufaycolor would seem to present valuable advantages. This consists in the mixture of light given by: A.hukusyuu-mobile.com/wp-content/bluetooth/1178-what-is.php
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The combined radiation consists of:. This lamp has now been standardized and its relative output of radiation should be constant after the lamp has been run continuously for 75 hours. During this ageing period it is quite possible that the line spectral emission ratio varies to a minor extent, but no data is available. It is proposed by Dufay-Chromex Ltd. On theoretical grounds there are good reasons to expect a marked improvement over the previously employed system.
Published by the U. Agfacolor Sensitizers and Colour Couplers. Chemical Formulae. We give below the formulae of the principal sensitizers and colour couplers used for Agfacolor negative and positive films:—. Paul Keck, formerly of Zeiss. This is a very interesting report upon some colorimetric work carried out in Germany on reproduction deviations found in the reproduction of colours by the Agfacolor films.
After a review of modern colorimetrical methods, he sums up the mathematical formulation of the problem of colour photography by A. Hardy, F. Wurzburg and others, in this next statement. Schultze and H.
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Hoermann of Agfa, Wolfen. Keck quotes from an unpublished paper by these authors. They calculated the reproduction of three different sets of samples:. The Oswald eight full colours. Eight saturated pigment samples from the Baumann-Prase Atlas. Eight spectrum wavebands of constant luminance. Generally the tristimulus values give the worst results. Here the RUCS distance was only , and for the pigments Sensitivities with large overlapping spectral curves give poor reproduction.
This is especially true for the tristimulus values of the spectrum used as sensitivities. Sensitivity curves calculated according to Hardy and Wurzburg give very good results if the negative parts, as well as the overlapping sections, are neglected. The reproduction is almost as good as before when optimum colours are used which do not cover the whole visible wavelength range. The best colour reproductions result in average deviations from in the RUCS system. Red and magenta chromaticities in general give rise to the largest differences and yellow hues correspond to the smallest ones.
The same authors have published measurements on colour reproduction by Agfacolor reversal film of a set of 12 highly saturated filters. The niters were also reproduced on Agfacolor Reversal Tungsten Type. Dominant wavelength and colorimetric purity of the originals and reproductions were measured.
The colorimetric purity values were transformed into excitation purity. For the 12 selected samples the dominant wavelengths and excitation purities are given in the accompanying Table The values under Dl and D2 refer to two exposures in daylight and A refers to the exposure to tungsten light. The distortions are serious, especially with blue and violet hues.
As far as luminance is concerned the transparency of the reproduction is always less than that of the original filter. The same authors measured the reproduction chromaticities of the same 12 filters as reproduced by the Agfacolor negative-positive process and also obtained comparison reproductions by printing Agfacolor positive with three separation negatives exposed through Agfa tricolor filters 40, 41 and The light source was ICI—A.
Narrow-cut tricolor filters were used for printing. The reproduction of blue and violet filters i, k and l, display larger deviation than did the reversal film.
The print made from the separation negatives was little better. Eight pigments of high saturation in the Baumann-Prase Color Atlas were reproduced by the reversal and by the negative-positive process. Results are given in the following Table. Note the dominant wavelength of No.
The reproduction of No. On the other hand No. In general, the Agfacolor process gave deviations about twice as great as by the best an additive system could yield. Reversal was slightly superior to negative-positive. This is an interesting question and there is not much data yet to help us to come to reliable conclusions. Masking is a pastime for mathematicians. The writer is firmly convinced that up to the present, a set of separation negatives represents by far the most reliable and accurate foundation.
Beam-splitter cameras are expensive, cumbersome, and delicate, but they give the technician an odd feeling of security after experience of the vagaries of monopack. Nevertheless negative-positive processes, such as Agfacolor, have their proper field of application and we must hope that one of the manufacturers will shortly revive its production. In the meantime physicists are welcome to cover pages with their symbols to prove that something can be done on paper which cannot be done in the laboratory.
Brock, who visited the Agfa film factory in June , stated in the report C. Trip No.
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Farben, Agfa Subsidiary Wolfen. Ranger and others, Jan. Final Reports Nos. Rose and Br. White T. Note: B. Cornwell-Clyne, Adrian : Colour Cinematography. This criticism based on the fact that Ryan did not mention Agfacolor. Only the American author James L. Limbacher gave some information on Agfacolor and listed many titles of feature films in his book Four Aspects of the Film New York Actually the history of Agfacolor is fairly unknown in the U.