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HANDBOOK OF PHOTOGRAPHY 



tively constant.) The negative-duplicating emulsion contains a yellow dye, which 

 dissolves in development, to increase resolving power by controlling light scattering, 

 extending latitude, and holding down maximum contrast. Like the background nega- 

 tive, the duplicating negative must be of extremely low grain. The speed is sufficient 

 for optical printing, in which the light reaching the unexposed film may be considerably 

 less than in contact printing. 



By reason of refinements in materials and processing, the quality of release prints 

 from duped negatives has been raised to a point where it is often indistinguishable from 



Fig. 16B. — Spectrogram of Agfa Supreme panchromatic negative No. 153 (tungsten). 



2.0 



10.2 m in: 



7.0 m in. 



Log Exposure 

 Fig. 17A. — D-logio E and time-gamma curves of Agfa Ultra-speed panchromatic nega- 

 tive No. 356. 



Fig. 17 B. — Spectrogram for Agfa Ultra-speed panchromatic negative No. 356 (tungsten). 



that of prints taken off original negatives, in spite of the fact that the duped negative 

 accumulates the defects of three different processings. 



Another type of negative differing markedly from panchromatic is the infrared 

 sensitized form, the processing and spectral characteristics of which are given in Fig. 

 17. The composition of the emulsion, it will be noted from the spectrogram, is such 

 that the film is blind in the green-yellow region, the response being confined to the 

 red and infrared and, at the other extreme, the blue. Such emulsions are useful in 

 penetrating haze, but, more frequently in cinematography, they are employed to secure 



