Thank you, gentlemen, for continuing to explain the complexities of tone reproduction to me. Stephen, I have now reviewed your paper "What is Normal", and the other paper that you recommended, "Exposure-Speed Relations and Tone Reproductions", and I have, also, re-read parts of BTZS, and WBM. I plan on finishing reading BTZS, and the other suggested items, and I have ordered a copy of "Sensitometry for Photographers" by Eggleston.
I am puzzled by how the flare/non-flare computations arrive at almost identical aim CIs: Stephen's practical flare model, and the WBM gradients, mentioned on page 212, especially as there is one other major, I think, difference in approaches. Stephen uses the generally accepted LER of 1.05 for Grade 2 paper. This, by ISO definition, only uses a portion of the available scale of a paper, notably not exceeding 90% of the available DMax. WBM carefully points out that "log exposure range of grade-2 paper is limited to 1.05, but this ignores extreme low and high reflection densities." and it suggests "We have no problem fitting a negative density range of 1.20 onto grade-2 paper, if we allow the low end of Zone II and the high end of VIII to occupy these paper extremes." WBM uses the figure of 1.2 in the calculation of aim average gradients on page 213.
Perhaps I am wrong in thinking so, but my observations of my own, and of other peoples' prints, suggest that a full range of paper DMax is often used and aimed for, and even enhanced further with Se toning. If we took the longer LER, as suggested by WBM, into the calculation of a contrast gradient using Stephen's approach, surely we would come up with a different set of aim CIs. Should we follow WBM advice, or was flare somehow part of the explanation?
I am confused by the apparent lack of consistency between testing based on old school, pre-ISO-change-in-1960 ZS, later improvements to ZS tests, WBM, and even Stephen's carefully thought through explanations, and BTZS. And I have not even thought much yet about the impact of enlarger flare.
Noticing the apparent disagreement between experts, in a discipline as old as photography, helps me understand why many experienced photographers and printers recommend not to go too deep into the logic of this matter, and just to rely on the graceful forgiveness of the process. Still, there is a part of me that would like to get my mind around it. Perhaps, in time, I will, or perhaps I was born too late to have a chance.
Last edited by Rafal Lukawiecki; 09-19-2012 at 07:36 AM. Click to view previous post history.