PRINTING PROCESSES 



421 



that- very few, if any, persons will be able to detect that distortion has entered into the 

 printing of a given negative. It is the aim of the paper manufacturers, however, to 

 make printing materials that are as near technically perfect as possible and at the 

 same time to make them practical to use. 



The exposure ranges that are often cited as being about 5 to 1 for a contrast paper 

 and about 50 to 1 for a soft paper are secured by measuring the exposure differences 

 required to produce certain density differences. If a considerable portion of the toe 

 region of the curve is taken into this calculation, the exposure range cited will be 

 greater than if only the truly straight part of the characteristic is considered, as one 

 may see from the curves in Figs. 7 and 8. These are characteristic of Defender B Velour 



Nega+ive 



-^ Brighi-ness range [<•- 

 ofsubjec-h =5.2 



--> 



Brighfness Range 

 of prinf=5.2 



h-- 



Fig. 6. — Theoretical curves relating brightness range of subject, opacity range of nega- 

 tive and brightness range of print. Here the product of negative and print gammas 

 (1.21 X 0.825) equals unity; a requirement for correct tone reproduction. 



Black (a projection paper) and of Apex (a Defender contact paper), 

 following table were taken from these curves: 



Table III. — Characteristics of Paper 

 Paper — Apex 



Data for the 



The "speed" here is taken as the exposure in meter-candle-seconds required to 

 produce a print density of 1.0. Thus the projection paper is seen to have a speed of 



