Don wrote this:
"Think about this for a moment, if you will. If we test and establish that a film such as TriX, for instance, is truly a EI 160 film (based on a .10 density in HC110 dil b). Then we place the low values in an exposure on a Zone III or IV. Aren't we in effect saying that irrespective of the manufacturers rating or Ansel's and Fred's edicts that this film needs to be exposed at EI 40 (Zone III placement) or EI 20 (Zone IV placement). Then when we have in our development testing placed our high value densities at 1.25 above FB+fog we have in effect shortened the entire scale of the film. This is a sure guarantee for flat and lifeless prints in my darkroom."
Lee wrote this:
"the way I interpret this is that the zone III is really at 80 and the zone IV is 110. Maybe I am not understanding properly. Certainly would not be the first time.
Don wrote this:
Lee, you raise an interesting point. Maybe my calculations are in error. This is how I arrived at the EI's that I originally posted. If we start with the EI of 160 for TriX, then each zone will be a doubling or halving of light reaching the film and consequently a doubling or halving of the EI. Thus I calculated Zone I as 160. Zone II as 80 (since the exposure is doubled), Zone III as 40 (again redoubled), and Zone IV as 20 (again redoubled). The EI is halved when the exposure is doubled.
Yes you are correct in that Ansel said 1.35 for diffusion sources and 1.25 for condensor sources. I did my originally testing of TriX according to those parameters. My experience still stands. The overall contrast is acceptable and the local contrast seriously sucks.