Just ask Jeeves about the neg to pos RMS conversion factor. Rule-of-thumb: neg RMS x 2.5. (Example: Neg of 4 x 2.5= 10 for pos). No explanation noted as to why the two film types are not based on the same scale. Much tech info avail if one cares to read it.
Jack --- Alin Flaider <[EMAIL PROTECTED]> wrote: > > Jack, > > In absolute terms, the negative emulsions have > finer grain than > positive. Indeed, Agfa's best negative, Portrait > 160 with it's > granularity of RMS 3.5 is obviously better than > the RMS 10 of their > best positive - RSX 50. The difference maintains > more or less at all > other manufacturers. > In real world though, the thicker layers of the > positive emulsion > accounts for higher densities that translate to > finer gradations in all > three colour channels. This comes at the expense > of the reduced > exposure range compared to the negative emulsion, > but given a > subject whose exposure range is covered by the > positive emulsion > latitude, the positive delivers a richer image > than the negative and > the continuity of tones hide its higher > granulation giving the > overall better appearance. > In the digital era, this becomes even more obvious > with the post > processing level of the scanned image: the lack of > tones of the > negative emulsion image is immediately apparent as > noise, sometimes > after as little as level adjustment and curve > manipulation to open > the shadows. Despite its smaller grain, the noise > gives the negative > film the contrary appearance. > In my limited experience, the only negative film > that comes close to > various positives (like Provia 100F, CT Precisa > 100, RSX 100, etc.) > in terms of rich image in tones is the Kodak RG50. > Too bad it became > "obsolete". [Flame disclaimer: note that I don't > discuss other > criteria like exposure latitude, colour linearity, > etc.; it's not > the end of the world if I cannot capture all the > subject's details, > to me a good picture should also suggest, not just > depict). > > Servus, Alin > > Jack wrote: > JD> I had a lab owner emphatically contend > that.."positive > JD> film of the same ISO has finer grain than > negative > JD> film". Didn't address b&w. > JD> We happened to be reviewing a b&w print at the > time > JD> and their existed a situation wherein the > subject > JD> couldn't be pursued (customers waiting). > JD> I've since emailed him for a follow-up on his > JD> recommendation that "b&w film be scanned as > positive > JD> film". > JD> If his answer (if received) is at all > decipherable, > JD> I'll forward it. > JD> Does anyone know or suspect what he may be > talking > JD> about? > JD> I've, also, read the RMS charts but, their > results > JD> don't appear to be comparable. > > > > JD> > __________________________________________________ > JD> Do You Yahoo!? > JD> Tired of spam? Yahoo! Mail has the best spam > protection around > JD> http://mail.yahoo.com > > __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
