Law for True Photographic Rendering of Contrast. 193 



The constant logi 2 "is arbitrary as we have said before, 

 and y= tan V 



Fig-. 6. 





^ L -8 E 2 



A low characteristic curve for the negative requires a 

 steep characteristic curve for the positive print. In fact 

 0i + 2 = ^0°, where Y and 2 are their respective inclinations 

 to the horizontal exposure axis. In real cases, onlv the 

 central part of the curve is straight (figs. 4 and 5). Since 

 the conjugate curve is obtained from the curve of the 

 positive simply by a change of origin and axes, the length 

 of the straight line portion in the two curves is the same, 



Phil. Mag. S 6. Vol. 38. No. 223. July 1919. 



