422 



HANDBOOK OF PHOTOGRAPHY 



about 100 times that of the contact paper (710 m.c.s. required to produce a density of 

 1.0 on the contact paper compared to 6.3 m.c.s. required for the projection paper; both 

 grades being medium). The exposure range was estimated by considering the portion 

 of the characteristic between a density 0.2 less than the maximum possible on the 

 paper and 0.2 above the minimum measurable density. These exposure ranges 

 would come more into line with the tables of such ranges already published if more of 

 the toe region of the characteristic were used in making the range estimate. Gamma 

 values were obtained in the customary manner, viz., the ratio between the change in 

 density to the change in the log exposure over the straight portion of the curve. 



1.4 



1.2 



t.O 



«0.8 

 o 



0.6 



0.4 



0.2 



0.545 0.696 0.846 0.996 1.147 1.797 1.448 1.598 1.749 1.899 2.05 



Log Exposure 

 3.508 4.966 7.02 9.91 14.03 19.82 28.06 39.63 56.11 79.25 112.2 

 Meter Cotndle Seconds 



Fig. 7. — Points on D-logio E curve used to calculate density range of paper. 



It will be noted that these papers have definite straight portions to the characteris- 

 tic, that the harder (more contrasty) papers have steeper characteristics, and that for 

 these papers the exposure range is less than for the softer papers. 



Effect of Curvature of Characteristic- — Since practical printing materials may have 

 appreciable curvature in their Z)-logio E characteristic, it is worth while to consider 

 what happens when either the exposure has been incorrect so that the lower or upper 

 bend is used or the brightness range of the subject is so great that both upper and lower 

 curves must be used. 



Suppose that the exposure has been insufficient to place the shadow portions of 

 the subject up on the straight part of the curve. The high lights, however, are cor- 

 rectly exposed. The opacit\^ ratios (density differences) in the high-light region will 



