I thought I would revive this thread with a somewhat cryptic note in Haist's sensitometry chapter regarding D-min (fog) in relation to the plotting of a characteristic curve, and what made me start to think about this and theoretical implications to ISO testing etc.
"In some cases the D-min has been subtracted from all densities, making the D-log E (H) curve touch the line of zero density."
As we know this is a common practice when people perform various types of Zone System tests for personal EI and contrast. It is advocated by Adams etc. The next sentence in Haist is:
"This practice, however, fails to take into account that fog silver is not distributed uniformly over all levels of image density."
Nothing more is said, but it got me thinking. The footnotes to this sentence reference two sources which may or may not have any relevance today:
R. B. Wilsey, "Fog Corrections in Photographic Densities," Phot. J., 65: 454 (1925)
H. A. Pritchard, "The Fog Correction of Photographic Densities: A Sensitometric Study," Phot. J., 67: 447 (1927)
Last edited by Michael R 1974; 10-17-2013 at 01:11 PM. Click to view previous post history.