That's not the point I'm challenging though. I'm saying that reducing exposure under these conditions is detrimental.
I think Stephen agreed with me earlier so I'l try to present this argument against reduced exposure again. I might be wrong but I don't think so. CPorter has said he's interested in practicality. I'm simply challenging the logic of something he's occasionally doing in practice under high subject flare conditions.
Given a film, zero flare and fixed processing procedures, a characteristic curve is generated for the film. That is the curve under those conditions. It is independent of the exposure we decide to give. If we have a subject under these hypothetical conditions (say a grey scale), more exposure moves the subject up the curve. Less exposure moves the subject down the curve. But the curve does not change.
Repeat this under a high flare scenario. The effect of subject flare is reduced contrast. The lowest negative densities are affected most. All other things being equal, compared with the zero flare curve, non-image forming light (ie flare) causes both an increase in density, and reduced contrast for exposure values below around Zone V. That is now the characteristic curve we have to work with. It is independent of the exposure we decide to give the film. As in the no-flare scenario, giving more exposure moves the subject (suppose it is the grey scale again) up the curve. Less exposure moves it down the curve. The shape of the curve doesn't change. So, if we reduce exposure, all we are doing is moving more of the subject into the lower part of the curve - where contrast is lower. It's not helping anything. It's just reducing local contrast for more of the subject values.
I'm simplifying here, but perhaps the key point that's being lost is that the flare light that "lifts" the shadow values is non-image forming light.
So I'll ask again - what is the purpose of giving less exposure? You might have a shorter print exposure time, but reduced local contrast in the shadow values in the negative - not a good thing from a Zone System perspective.
So I actually disagree with the notion effective speed is increased by flare effects. Perhaps the speed "point" is increased, but local contrast in the shadows is decreased. If speed is a means to an end (ie sufficient local contrast in the shadows), we've lost more than we've gained, and this is compounded by reducing exposure.
Andreas - you are not alone. I'm getting a little better at this (slowly) but I still often get lost in the various charts, diagrams etc. Stephen and Bill are much better at this than I am. I need to take a few days and slowly go through Stephen's stuff (not just this thread but several others).
Last edited by Michael R 1974; 01-29-2013 at 08:40 AM. Click to view previous post history.