Stephen, if you don't mind the diversion back to speed determination, I'd like to list some questions and observations based on the papers you sent me. At the outset I must admit at first the graphs on page 325 of the Nelson/Simonds really surprised me and kind of turned my hypothesis upside down regarding the best speed method for my work. As I went through your paper the issue became a little clearer to me, although I still have questions. And I might now have shifted my preference back to fixed density vs fractional gradient when it comes to developing for reduced contrast. Still not entirely sure. First a few questions:
1. In Nelson/Simonds, they state the interval 1.3 Log E (H) interval was chosen “in order that D2 would be approximately equal to the highlight density in the first excellent negative of an average scene”. Can you explain this?
2. In your paper you state the ISO speed point falls 3 1/3 stops below the meter calibration point and shadow exposure falls 4 1/3 stops below. I’m confused by both these intervals.
Now to the “issue” I alluded to, which your paper addresses in the example illustrating how with lower or higher than average delta Ds the Delta-X speeds rounded to the same number (the “compensation effect”).
It occurs to me, the print evaluation studies originally used in deriving 0.3G involved exposures of average scenes. So, to me, it would mean in the context of the tests, developing the films to lower gradients (for example) would have constituted “errors” to be corrected with an increase in paper grade – rather than deliberate attempts to accommodate a higher than normal subject luminance range. This could explain why I was initially startled by the six graphs on p.325. Before going into this, I had actually expected at least some of the print judgment speeds and 0.3G speeds to be lower than the fixed density speeds (eg: the long toe, low gradient curves). But this is the opposite of what was concluded in the print evaluation studies. While the math made sense to me, intuitively the graphs just didn’t look right – unless one simply increased the paper grade to effectively normalize say the bottom two curves in Fig.2. This is my take on why the fractional gradient method is not more concerned about a precise contrast. A constant relationship of 0.3G seems to work in print judgment tests, apparently regardless of how low the absolute toe contrast is, because a correction via increase in paper grade would bring both the toe G and average G up. I think this is sort of a different way of saying the same thing as the possible explanation you outline in your paper for why fractional gradient is not more concerned with a target contrast, and why the Delta-X film speed stays relatively constant with deviations in delta D.
Another possible explanation for why ZS testing typically results in lower EIs than ISO speeds – even when targeting a normal gradient – concerns the shape of a typical modern film curve in relation to the Delta-X criterion of .8 delta D over a 1.3 log H interval. But before I get into that, I really need a better understanding of the intervals in question 2 above. I think those are key to my understanding.
Hopefully I’m not too off the rails here…
Thanks again for bearing with me. I'm not the quickest at "getting" this stuff.
Last edited by Michael R 1974; 03-09-2013 at 07:41 PM. Click to view previous post history.
Reason: typos and clarity