

Law for True Photographic Rendering of Contrast. 191 



the characteristic o£ -the conjugate plate also. We may 

 express the transformation most easily by saying that if the 

 characteristic curve Di against log Ej be drawn on tracing- 

 paper and be then viewed from the back so that the first 

 origin is at the top right hand corner, the curve, as it thou 

 appears, is the characteristic curve of the conjugate plate. 

 Such a curve is shown in fig. 5 for comparison. 



D,^ 



It should be carefully remarked that the new origin 0" 

 may be any point whatever. But it must not be forgotten 

 that the constant amounts by which it is shifted in the 

 two directions are connected with the viewing light and 

 printing light. In fact, 



00'= log [viewing light -^K] = log V — log K, 

 0'0"= log [printing light] = log P. 



To choose the point 0" is equivalent to deciding upon 

 particular values for the printing and viewing lights and the 

 reduction factor K. The more nearly K is to unity the more 

 nearly will the light from the positive be not only the same 

 in gradation as that from the subject but also the same in 

 absolute intensity. 



When we make a print we arrange our exposure so that 

 the curve of the paper is in the best position with reference 

 to the axis of log E 2 to be brought by development to fit the 



