PRINTING PROCESSES 



423 



be directly proportional to the subject brightness ratios. But because of the curvature 

 two shadow regions differing by, say 3 to 1 in brightness, will not produce opacity ratios 

 of this value (when the characteristics of the printing material are such that t = !)• 

 They will produce less than a 3 : 1 ratio in opacity because over the curved region it 

 requires more than a 3: 1 exposure ratio to produce a 3: 1 opacity ratio. 



2.0 



1.8 



1.6 



14 



ml.O 



c 



o 



0.8 



0.6 



0.4 



0.2 







1.551 1.701 1.852 2.002 2.153 2.304 2.454 2.604 2.755 2.905 3.056 3.206 3.357 



Log Exposure 

 35.56 50.25 71.12 100.5 142.2 201.4 284.4 401.8 568.9 803.5 1138 1607 2276 



Meter Coindle Seconds 

 Fig. 8 a. — Contact-paper characteristics. Grade 00 is soft; 55 is extra contrast. 



If, on the other hand, the shadows are exposed so that they lie on the straight 

 part of the curve, the high lights may be overexposed, extending up beyond the straight 

 portion of the H and D curve. Now they will be distorted since brightness ratio of 

 3:1 will not produce a 3: 1 ratio in opacity; they will produce less than this variation. 

 In this case the shadows of the negative (or print) will be correct and the high lights 

 will be incorrect (blocked up). 



In negative making, correct exposure is usually considered as that exposure which 

 will get the shadows up on the straight portion of the curve. Then the straight part 

 of the curve has sufficient length for the high lights not to reach the shoulder. But if 

 appreciably greater exposure is given to the negative, the high lights may be blocked 



