Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 (Tek) 9/28/84 based on 9/17/84; site tekig4.UUCP Path: utzoo!linus!philabs!cmcl2!seismo!bbnccv!harvard!talcott!panda!genrad!decvax!tektronix!tekig5!tekig4!briand From: briand@tekig4.UUCP (Brian Diehm) Newsgroups: net.rec.photo Subject: Re: Is OM-4 Junk? Message-ID: <212@tekig4.UUCP> Date: Mon, 12-Aug-85 20:25:52 EDT Article-I.D.: tekig4.212 Posted: Mon Aug 12 20:25:52 1985 Date-Received: Sun, 18-Aug-85 23:47:43 EDT References: <1520@trwrba.UUCP> <9414@ucbvax.ARPA> <471@tymix.UUCP> <1415@peora.UUCP> <475@tymix.UUCP> Organization: Tektronix, Beaverton OR Lines: 37 > In article <1415@peora.UUCP> jer@peora.UUCP (J. Eric Roskos) writes: > >> If you use Ilford XP1, you can use Zone System doctrine to a limited degree > >> by changing the ASA rating for each shot. Exposed at ASA 100, the neg will > >> have much lower contrast than it will when exposed at ASA 400. > > > >Isn't this just an effect of nonlinearities in the "toe" region of the film's > >characteristic curve? I.e., if you underexpose the film and develop it > >normally, most of the exposure will end up down in the region where the > >slope of the curve is less; which is, of course, exactly the definition of > >low contrast (please, no flames on the definition of "contrast index," I > >know the CI includes the nonlinear regions.). > > > >A disadvantage of this method, though, would be exactly that the curve > >IS nonlinear; so differences between two lower levels of luminance would > >be less pronounced than between two higher levels. This would tend to > >produce a loss of detail in the shadows. > > Nope, I was not talking about working at the toe (low exposure end of the > curve) but about the other end ( would you call that the heel :-)?) Rate > XP1 at ASA 100 and you will get a very dense negative, but because of the > film's incredible dynamic range, the highlights will not block up. You > will, however, be on a section of the curve that has a lower gamma than the > section you would encounter at ASA 400. You will also get much finer > grain. However, because of the density, you might not like the long > printing time. > > Dick Delagi, in his recent article on XP1 in Popular Photography, said that > he originally decided to shoot the stuff at ASA 200 in order to get finer > grain (this stuff gets grainy where the negative is thin!!!), but reverted > to ASA 400 because of the loss of contrast and excessive density from > over-exposure. This implies that if your intent is to reduce contrast, you > can achieve it by over-exposing. The reason you can do this with XP1 and > not with conventional film is that the high end of the H & D curve flattens > out very gradually, whereas the curve for conventional film comes to a > rather abrupt halt. *** REPLACE THIS LINE WITH YOUR MESSAGE ***