>I was hoping someone that really knows about this would answer, but it
>doesn'tlook too promising. So, I will suggest that you take a look at the
>book:Davis, Phil, Beyond the Zone System 3rd Ed., Focal Press, 1993. I
>think that what you are looking for can be found on page 29.
Wayde, I think there have been a number of informative comments posted -
perhaps you have been away from the list?
One of the interesting points about the newer emulsions (Delta and T-Max)
is that they appear to have long more or less straight line curves above a
fairly short toe, so gamma once more becomes a useful measurement.
Also it is important to realise that the 'upper density point' mentioned in
this is a point that has significance only for the purpose of defining the
contrast index - it is certainly not a limit on the useable part of the
curve.
Similarly the 0.1 above base fog is an arbitrary point used as the bottom
value for determining contrast index. You might find you could distinguish
0.05 above base fog when printed on a particular material.
I think I have already a month or two ago suggested a relatively accessible
book on this list, but I'll repeat it:
Sensitrometry for Photographers, Jack Eggleston, Focal Press (London &
Boston) 1984.
isbn 0 240 51144 1
Sensitrometry is of course what is really beyond the Zone System!
Peter Marshall
Fixing Shadows and elsewhere:
http://faraday.clas.virginia.edu/cgi-uva/cgiwrap/~ds8s/Niepce/peter-m.cgi