Archived posting to the Leica Users Group, 2006/02/05
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]one can define an objective film speed as well as development time as those such that a zone I exposure (4 stops underexposed) is on the negative about 0.10 above the film base plus fog on a densitometer, and zone VIII (3 stops overexposed) is about 1.25 above film base plus fog. adams and picker talk about this in their books, adams has graphs of various films in _the negative_. you can take a 400 film, shoot it at 1600 and develop the heck out of it, and your zone V may fall with a density of around 0.75, but your zone I will be inseperable from fog and zone VIII might be blocked. it's not to say this is ill-advised, but the film's "true" speed will not be 1600, it would be a 400 film underexposed and developed to the point where the midtones fall about where a "true" 1600 film's midtones would fall. -rei On Feb05 17:46, Matt Powell wrote: > On 2/5/06, Didier Ludwig <rangefinder@screengang.com> wrote: > > > > >... neither Delta 3200 nor TMax 3200 is a true 3200-speed film. > > Matt > > What do you ecaxtly mean with "not a true 3200-speed film"? Just > > curious. > > Didier > > However ISO is measured (I believe it's shadow density at > something-or-other blah blah blah, I don't do testing of that kind), > neither of the 3200 films is a 'true' 3200 ISO (as Tri-X is a true 400 > in certain developers, etc.). TMZ or Delta3200 at 3200 is underexposed > (and then push-processed). > > This is all badly explained, I'm sure. > > -- > MP > wooderson@gmail.com > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information -- Rei Shinozuka shino@panix.com Ridgewood, New Jersey