Collin, In practical terms to you as a photographer the toe (and also the shoulder) of a film's characteristic curve are regions in which the density difference for a given exposure difference is less than it is for the same exposure difference in the straight line region. The tones in these areas will be compressed and will print with low contrast when the average contrast of the whole print is correct.
A longer but still simplified explanation is that the characteristic curve of a film and developer combo (and the curve is different when a different developer and/or degree of development is used) has three main regions: the toe; the straight line portion; and the shoulder. To understand the toe you also need to know what the straight line is. My knowledge was learned, and mostly forgotten, during the ASA/DIN years so things could be slightly different now that we're under the ISO system of film speed and contrast measurement, but I believe the concepts are very similar if not identical. The straight line got its name under older systems of speed and contrast measurement such as Hurter and Driffield (up to 1950s) when it was very literally the region of the curve that looked straightest, when a straight line was drawn through it the divergent regions at the bottom and the top of the curve were decreed to be toe and shoulder. Under the ASA/DIN system the boundary between toe and shoulder was newly defined to be at an arbitrary transmissive density above base plus fog (or D-min). Base plus fog is the density of ~absolutely~ unexposed film that has been developed to the specification being plotted as a characteristic curve. Therefore every point above this until another arbitrary point (which I've forgotten, either a prescribed number of stops or a prescribed transmissive density below D-max) were decreed to be the straight line, and thus all points of the curve below and above are the toe and the shoulder. Incidentally, it's been said on this list that stated film speeds were doubled sometime in the 1950s with the explanation that it was considered that film latitude was sufficient to enable a stop less exposure. Not strictly correct. It just happened that at that time the H&D system gave way to the ASA/DIN system and the new numbers reflected the different methods of speed determination used by the older and newer systems. Regards, Anthony Farr ----- Original Message ----- From: "Collin Brendemuehl" <[EMAIL PROTECTED]> > What is meant when describing a film's "toe"? > Does anyone know of a web site with these > definitions elaborated upon? > > > -- > > Collin Brendemuehl, KC8TKA - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
