Quote Originally Posted by Michael R 1974 View Post
Is it then fair to say measurements for a particular film/developer based on sensitometry (such as ISO speed, contrast index, gamma etc.) are concerned strictly with absolute densities at exposure levels, rather than image or "useful" densities at exposure levels? In other words sensitometric measurements are concerned with the total density at any level of exposure regardless of how much incremental density is directly a result of the exposure?
Well, I would be most interested in the signal density. The density I can use to make an image on a print.

So fog, due to light scatter inside the camera, has to be considered when it is part of the negative. So I might be looking at 1.2 density with 0.35 fog under it that I have to print through by doubling print exposure time. Despite the fact I have a low base+fog for that sheet. For example if my base+fog was 0.05 (an example of my B+F from 4x5 TMY2).