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HANDBOOK OF PHOTOGRAPHY 



of the shorter wavelengths decreases rapidly as the voltage is lowered, so that fluctua- 

 tions in line voltage may cause considerable changes in printing time, even though the 

 visual brightness is not noticeably affected. 



Contrast, Effect of Development. — Owing to the thinness of coating and the fine 

 grain, paper emulsions develop rapidly. During the very first period of development 

 the contrast increases with time as in the case of negative emulsions. During this 

 period, however, the shadow density is low and the characteristic curve is badly dis- 

 torted. As the shadow density approaches the maximum black, the curve is straight- 

 ened out somewhat and then begins to move to the left, with no change in slope or 

 contrast and with little or no further increase in shadow densitJ^ These effects vary 

 slightly with the different types of emulsions, for instance, with some bromide and 

 ohlorobromide papers, the contrast does increase slightly on continuing development 

 after the maximum black is reached. 







2.1 



2.4 2.7 3.0 



0.3 0.6 09 1.2 1.5 1.8 



Log Exposure, Log Ey 



Fig. 14. — Typical Z)-logio ^ curves for chloride paper. The lettered curves represent 

 different times of development. These curves show that development afTects the speed, 

 but does not affect the gamma appreciably. 



The effect of time of development on the characteristics of chloride, chlorobromide, 

 and bromide types of papers is shown, respectively, in Figs. 14, 15, and 16. Time of 

 development increases, for the various curves, in alphabetical order. 



In general, however, since it is necessary to develop sufficiently to reach the maxi- 

 mum black in order to avoid uneven development, muddy shadows, and distorted 

 tone rendering, the contrast cannot be controlled in development. On the other hand, 

 since there is usually a period between the time when the maximum black is reached 

 and when development fog appears, during which the densities continue to increase 

 without changing contrast, it is possible to correct for slight variations in exposure by 

 adjustment in development. This exposure-development latitude varies considerably 

 between the different papers. 



It has been suggested that the contrast of a particular paper could be varied by 

 changing the developer formula. While in isolated cases this might be possible, it has 

 been shown that the variations normally obtained are less than the differences between 

 two adjacent contrast grades of the paper. ^ 



Pa-per Contrast. — As little or no control of contrast is possible during development, 

 many of the papers are supplied in several degrees of contrast. In the case of negative 



> BENKDirT, H. C, Facts and Foibles in Photography, Camera Craft, 43, 226 (1936). 



