Hi Stephen, thanks for your comprehensive reply. I would really love for Ralph to contribute to this discussion as he would have much to say on this topic he has devoted so much of his time, his book and this thread to it.

Your replies directly challenge his approach and the method from his book (WBM) which I had put plenty of trust in and was in the process of carrying out when your replies threw a spanner in my works.
Also, because Ralph has plenty of respect here and elsewhere, I find myself still aligned to his methods but am being forced to understand this more than I expected and come to my own conclusion if I am to break allegiance with what he does and recommends.

In his absence and prior to me digesting the pdfs you attached I don't expect to add much value to this thread. I might have more questions than answers I think. For now I will just add a few comments and go away and read your pdfs, and I will PM you my email address so you can send me "Simple Methods for Approximating the Fractional Gradient Speed of Photographic Materials"

Quote Originally Posted by Stephen Benskin View Post
Peter,
Okay, first we have to make sure we are referencing the same material. I believe you are using the pdf file from the Beyond Monochrome's website entitled "Testing Film Speed and Development." If you are then you also must be referring to fig 1 on page one of the document. And if that is the case, you are mistaking the log-H range for negative density range. Your use of the term "nomograph" if referring to figure 1 also confused me because I didn't think the term applies to that type of graph. It may, but in my earlier response, I was referencing the fig on page 140 of the first edition of Ralph's book.
Actually I was referencing the nomograph on p. 140 of WBM. There is a similar version of it on p. 66 of Stroebel's book "Basic photographic materials and processes" (p. 66 here) (which in turn was taken from a Kodak Publication from 1976) but the neg density ranges that nomograph lists differ from the one in WBM by quite a bit. e.g. the ISO std CI of 0.57 (in 1976) matches a neg dens range of 1.05, but in Relph's nomograh the ISO std of 0.58 matches a neg. dens. range of 1.29 (which I rounded up to 1.30 and used that in the formula I gave above.

Now why do the two nomographs differ so much ? I think it is because Ralph made a different assumption than that in the footnote (*) of p. 66 which reads "these are the typical negative density ranges that result when normal luminance range subjects (7 stops range) are exposed with moderate flare level lenses and developed to the contrast index shown in the left scale".

For now I don't understand enough to comment on the rest of your post except the last part where you write:

Quote Originally Posted by Stephen Benskin View Post
Ralph likes to use a negative density range of 1.20 for normal. His normal CI (average gradient) is also 0.58. As both aim Contrast Indexes are identical, that means that any scene photographed and developed to a CI of 0.58 is going to be the same on the negative. How is this possible with different aim negative density ranges?

Ralph's model - 1.20 / 2.1 = 0.57

Flare model - 1.05 / (2.2 - 0.40) = 0.58
Basically my only comment here is to Ralph: Help me out here please !!